13D Filing: Oaktree Capital Management and Oaktree Strategic Income Corp (OCSI)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 1)*

Oaktree
Strategic Income Corporation

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

67402D 104

(CUSIP Number)

Todd E. Molz

Managing Director and General Counsel

Oaktree Capital Management, L.P.

333 South Grand Avenue, 28th Floor

Los Angeles, California 90071

(213) 830-6300

With a copy to:

Gary I.
Horowitz

Rajib Chanda

Simpson Thacher & Bartlett LLP

425 Lexington Avenue

New
York, New York 10017

(212) 455-2500

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

March 7, 2018

(Date
of Event Which Requires Filing of this Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e),
240.13d-1(f) or 240.13d-1(g), check the following box.  ☐

Note: Schedules filed in paper format shall
include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7(b) for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be
deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (the Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).

CUSIP No. 67402D 104

CUSIP No. 67402D 104

CUSIP No. 67402D 104

CUSIP No. 67402D 104

CUSIP No. 67402D 104

CUSIP No. 67402D 104

This statement on Schedule 13D originally filed with the Securities and Exchange Commission on July 21, 2017
(the Original Statement) by Oaktree Capital Management, L.P. (Oaktree) and the other persons named therein is hereby amended and supplemented by this Amendment No. 1 to Schedule 13D. Capitalized terms used
herein and not otherwise defined have the meanings assigned to such terms in the Original Statement. Except as otherwise provided herein, each Item of the Original Statement remains unchanged.

Item 1 of the Original Statement is hereby amended and restated in its entirety as
follows:

The securities to which this statement on Schedule 13D relates are the shares of common stock, par value $0.01 per share (the
Common Stock) of Oaktree Strategic Income Corporation, a Delaware corporation (the Issuer), with principal executive offices at 333 South Grand Avenue, 28th Floor Los Angeles, California 90071.

Item 2 of the Original Statement is hereby amended and restated in its entirety
as follows:

(a) – (c) and (f)

This Schedule 13D is being filed jointly, pursuant to an amended and restated joint filing agreement, by (i) Oaktree, a Delaware limited
partnership and a registered investment adviser under the Investment Advisers Act of 1940, as amended, whose principal business is to provide investment advisory services to investment funds and accounts; (ii) Oaktree Holdings, Inc., a
Delaware corporation (Holdings, Inc.), whose principal business is to serve as, and perform the functions of, the general partner of certain entities affiliated with the Reporting Persons and to hold limited
partnership interests in such entities; (iii) Oaktree Capital Group, LLC, a Delaware limited liability company (OCG), whose principal business is to act as the holding company and controlling entity of each of the general
partner and investment adviser of certain investment funds and separately managed accounts; (iv) Oaktree Capital Group Holdings GP, LLC, a Delaware limited liability company (OCGH GP), whose principal business is to serve as,
and perform the functions of, the manager of OCG; Oaktree Capital I, L.P., a Delaware limited partnership (Oaktree Capital I), whose principal business is to serve as, and perform the functions of the general partner of Oaktree
Fund GP I, L.P. and to invest in securities; (vii) OCM Holdings I, LLC, a Delaware limited liability company (Holdings I), whose principal business is to serve as, and perform the functions of, the general partner of Oaktree
Capital I and to hold limited partnership interests in Oaktree Capital I; and (viii) Oaktree Holdings, LLC, a Delaware limited liability company (Holdings and, together with Oaktree, Holdings, Inc. OCG, OCGH GP, Oaktree
Capital I and Holdings I, the Reporting Persons), whose principal business is to serve as, and perform the functions of, the managing member of Holdings I.

The Reporting Persons have entered into an amended and restated joint filing agreement, dated as of March 12, 2018, a copy of which is
attached hereto as Exhibit 1.

Set forth in the attached Annex A is a listing of the directors, executive officers, investment
managers, managers, members and general partners, as applicable, of each Reporting Person (collectively, the Covered Persons), and Annex A is incorporated by reference into this Item 2. Except as set forth in Annex
A, each of the Covered Persons that is a natural person is a United States citizen.

The principal business address of each of the
Reporting Persons and each Covered Person is c/o Oaktree Capital Group Holdings GP, LLC, 333 South Grand Avenue, 28th Floor, Los Angeles, California 90071.

(d) and (e)

During the
last five years, none of the Reporting Persons and, to the best of their knowledge, none of the Covered Persons: (i) has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors); or (ii) has been a
party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating
activities subject to, federal or state securities laws or finding any violation with respect to such laws.

Item 3 of the Original Statement is amended and
restated in their entirety as follows:

Beneficial ownership of the shares of Common Stock set forth on the cover pages to this
Schedule 13D (the Subject Equity) is being reported on this Schedule 13D solely because the Reporting Persons may be deemed to have beneficial ownership of the Subject Equity as a result of (i) the relationships and matters
described under Item 6 of this Schedule 13D and this Item 3 and/or (ii) purchases of shares of Common Stock by Oaktree Capital I, as applicable.

On July 13, 2017, Oaktree entered into the Voting Agreement described in Item 6 of this Schedule 13D with Fifth Street Holdings L.P.
(FSH), Leonard M. Tannenbaum, the Leonard M. Tannenbaum Foundation and the Tannenbaum Family 2012 Trust (collectively, the Tannenbaum Stockholders) pursuant to which each of the Tannenbaum Stockholders agreed to
vote their shares of Common Stock at the direction of Oaktree. The Tannenbaum Stockholders entered into the Voting Agreement as condition of and an inducement to Oaktrees willingness to enter into the Asset Purchase Agreement described in Item
6 of this Schedule 13D. Upon the acquisition of any additional shares of Common Stock by the Tannenbaum Stockholders, such additional shares will be included under the Voting Agreement, and the Reporting Persons may be deemed to have beneficial
ownership of such additional shares, if any, to the extent such Reporting Person is covered by the Voting Agreement.

No payments were
made by or on behalf of any Reporting Person in connection with the execution of the Voting Agreement.

Beginning on December 13,
2017, Oaktree Capital I used available funds to purchase shares of Common Stock.

Items 5(a), 5(b) and 5(c) of the Original Statement are amended
and restated in their entirety as follows:

Information concerning transactions in the shares of Common Stock effected by the Reporting
Persons during the past sixty days is set forth in Annex B hereto and is incorporated herein by reference. All of the transactions in the shares of Common Stock listed in Annex B hereto were effected in the open market.

As a result of the Voting Agreement described in Item 6 of the Original Statement and Item 3 above among Oaktree and the Tannenbaum
Stockholders, Oaktree may be deemed to be beneficially own 7,983,925.62, or approximately 27.1%, of the issued and outstanding shares of Common Stock, which shares of Common Stock are held by the Tannenbaum Stockholders (the Tannenbaum
Shares).

As a result of Oaktree Capital I purchasing 392,000 shares of Common Stock in the open market (the Oaktree
Shares), Oaktree Capital I may be deemed to beneficially own 392,000, or approximately 1.3%, of the issued and outstanding shares of Common Stock.

Holdings, Inc., in its capacity as the general partner of Oaktree, has the ability to direct the management of Oaktrees business,
including the power to direct the decisions of Oaktree regarding the voting and disposition of securities beneficially owned by Oaktree. Therefore, Holdings, Inc. may be deemed to have indirect beneficial ownership of the Tannenbaum Shares.

OCG, in its capacity as the sole stockholder of Holdings, Inc., has the ability to appoint and remove directors of
Holdings, Inc. and, as such, may indirectly control the decisions of Holdings, Inc. regarding the voting and disposition of securities beneficially owned by Oaktree. Additionally, OCG, in its capacity as the sole stockholder of Holdings,
Inc., has the ability to direct the management of Holdings, Inc.s business, including the power to direct the decisions of Holdings, Inc. regarding the voting and disposition of securities beneficially owned by Oaktree. Therefore, OCG may be
deemed to have indirect beneficial ownership of the Tannenbaum Shares.

In addition, OCG, in its capacity as managing member of Holdings, has the ability to direct the
management of Holdings business, including the power to direct the decisions of Holdings regarding the voting and disposition of securities held by Holdings. Therefore, OCG may be deemed to have indirect beneficial ownership of the Oaktree
Shares.

OCGH GP, in its capacity as the manager of OCG, has the ability to appoint and remove directors of OCG and, as such, may
indirectly control the decisions of OCG regarding the voting and disposition of securities beneficially owned by Oaktree. Therefore, OCGH GP may be deemed to have indirect beneficial ownership of the Tannenbaum Shares and the Oaktree Shares.

Holdings I, in its capacity as the general partner of Oaktree Capital I, has the ability to direct the management of Oaktree Capital Is
business, including the power to direct the decisions of Oaktree Capital I regarding the voting and disposition of securities held by Oaktree Capital I. Therefore, Holdings I may be deemed to have indirect beneficial ownership of the Oaktree Shares.

Holdings, in its capacity as the managing member of Holdings I, has the ability to direct the management of Holding Is business,
including the power to direct the decisions of Holdings I regarding the voting and disposition of securities held by Holdings I. Therefore, Holdings may be deemed to have indirect beneficial ownership of the Oaktree Shares.

Neither the filing of this Schedule 13D nor any of its contents shall be deemed to constitute an admission by any of the Reporting Persons
that it is the beneficial owner of any of the shares of Common Stock referred to herein for the purposes of Section 13(d) of the Act, or for any other purpose, and such beneficial ownership is expressly disclaimed.

To the actual knowledge of the Reporting Persons, none of the Covered Persons directly owns any shares of Common Stock, other than Bruce A.
Karsh, who directly owns 25,000 shares of Common Stock, and John B. Frank, who directly owns 11,876 shares of Common Stock; provided, however, that because of each Covered Persons status as an investment manager, manager, general partner,
director, executive officer or member of a Reporting Person, a Covered Person may be deemed to be the beneficial owner of the shares of Common Stock beneficially owned by such Reporting Person. Each of the Covered Persons disclaims beneficial
ownership of the shares of Common Stock reported herein, and the filing of this Schedule 13D shall not be construed as an admission that any such Covered Person is the beneficial owner of any securities covered by this statement, other than Messrs.
Karsh and Frank for their respective directly owned shares of Common Stock.

Item
6 of the Original Statement is hereby supplemented by adding the following sentence immediately after the last sentence thereof:

On
October 17, 2017, Oaktree closed the transactions contemplated by the Asset Purchase Agreement pursuant to which Oaktree has become the new investment adviser to each of the Issuer and Oaktree Specialty Lending Corporation.

SIGNATURE

After reasonable inquiry and to the best of its knowledge and belief, the undersigned certifies that the information set forth in this statement is true,
complete and correct.

Dated as of March 12, 2018

ANNEX A

Oaktree Capital Group Holdings GP, LLC

Oaktree Capital
Group Holdings GP, LLC is managed by an executive committee. The name and principal occupation of each of the members of the executive committee of Oaktree Capital Group Holdings GP, LLC and its executive officers are listed below.

Oaktree Capital Group, LLC

The name and principal occupation of each of the directors and executive officers of Oaktree Capital Group, LLC are listed below.

Oaktree Holdings, Inc.

The name and principal occupation of each of the directors and executive officers of Oaktree Holdings, Inc. are listed below:

Oaktree Capital Management, L.P.

The general partner of Oaktree Capital Management, L.P. is Oaktree Holdings, Inc.

Oaktree Holdings, LLC

The managing member of Oaktree
Holdings, LLC is Oaktree Capital Group, LLC.

OCM Holdings I, LLC

The managing member of OCM Holdings I, LLC is Oaktree Holdings, LLC.

Oaktree Capital I, L.P.

The general partner of Oaktree
Capital I, L.P. is OCM Holdings I, LLC.

ANNEX B

The following table sets forth all transactions in shares of Common Stock by the Reporting Persons in the past sixty days. All prices per share exclude
commissions. All transactions were open market brokered transactions.

EXHIBIT 1

AMENDED AND RESTATED JOINT FILING AGREEMENT

Pursuant to Rule 13(d)-1(k)(1) promulgated under the Securities Exchange Act of 1934, as amended, each of
the undersigned acknowledges and agrees that the foregoing statement on Schedule 13D is filed on behalf of the undersigned and that all subsequent amendments to this statement on Schedule 13D shall be filed on behalf of the undersigned without the
necessity of filing additional joint acquisition statements. Each of the undersigned acknowledges that it shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information concerning it contained
therein, but shall not be responsible for the completeness and accuracy of the information concerning the others, except to the extent that it knows or has reason to believe that such information is inaccurate.

Dated as of March 12, 2018.