Donovan struck twice in the Galaxy's 4-1 win over Philadelphia Union, while he also set up LA's opening goal, just three days after the 32-year-old missed out on a spot in the United States' final squad for the FIFA World Cup.
Leonardo and Galaxy skipper Robbie Keane scored the other goals for LA, while Maurice Edu - another casualty of Jurgen Klinsmann's cull on Thursday - struck an 89th-minute penalty for Philadelphia.
Galaxy needed just over a minute to take the lead at the Stubhub Center with Leonardo heading Donovan's free-kick past Union goalkeeper Zac MacMath.
The home side continued their strong start with Keane producing an audacious chip that hit the bar and then firing a long-range shot that MacMath held onto.
Galaxy had to wait until three minutes into the second half to double their lead, however, with Donovan releasing Keane down the right and then burst into the penalty area to tap the Irishman's low cross in at the back post.
The goal took Donovan to 135 in the MLS, taking him clear of Jeff Cunningham (134), who played for five clubs including Columbus Crew and FC Dallas between 1998 and 2011.
It also ended Donovan's scoring drought that had stretched back to October.
Keane took advantage of Sheanon Williams' terrible back-pass effort in the 63rd minute, beating MacMath in a one-on-one situation, before Donovan completed his brace with nine minutes left, again playing a one-two with his Irish strike partner, before firing into the net from near the penalty spot to take his MLS tally to 136.
The win took Galaxy up to sixth in the Western Conference with 15 points, two ahead of San Jose Earthquakes and two behind fifth-placed Vancouver Whitecaps, while Union are second-bottom in the East with 11.
In the other MLS game on Sunday, Khari Stephenson scored twice for San Jose as they accounted for Houston Dynamo 3-0.
The Earthquakes took the lead in front of their home crowd in the 38th minute after Houston goalkeeper Tally Hall picked up a back pass from teammate David Horst.
Shea Salinas then rolled the indirect free-kick to Stephenson, who fired the ball into the bottom corner of the net, while the 33-year-old Jamaican converted a spot kick in the 58th minute to give San Jose a 2-0 lead.
Atiba Harris scored San Jose's third goal in the 70th minute, winning an aerial challenge with Hall on the edge of the box, before knocking home the rebound after his header came back off the post.
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