Betts has 34 homers this season, including three in this series, which ended on Saturday as Major League Baseball sought to avoid the expected arrival of Hurricane Hilary on Sunday.
Josh Bell homered for Miami's only run in Saturday night's game.
Julio Urias (11-6) earned the win, allowing just five hits, no walks and one run in seven strong innings, lowering his ERA to 4.15. He is 4-0 with a 1.44 ERA this month.
Urias got out of a couple of jams, including two on and no outs in the third; and runners on second and third with two outs in the seventh.
Braxton Garrett (7-4) took the loss, allowing five hits, no walks and three runs in six innings. The Marlins are 18-7 when starting Garrett this year.
Miami opened the scoring in the first inning as Bell swung at a 1-0 fastball and drove the pitch 431 feet to center. The exit velocity was 110 mph.
The Dodgers tied the score in the second inning as Amed Rosario doubled and scored on Enrique Hernandez's two-out, opposite-field single to right. Hernandez hit a 2-2 fastball for the key hit.
Betts hit his first homer of the night in the third inning, giving the Dodgers a 2-1 lead with his 402-foot blast to left. Betts connected on a 2-1 fastball up in the zone.
In the fifth, Betts did it again, driving a 2-1 sinker 419 feet to left-center field.
The Marlins threatened in the ninth, getting singles by Jake Burger and Avisail Garcia off of Graterol. But with two outs and runners on second and third, Graterol got Jesus Sanchez on a slow roller to Hernandez at third. The Marlins challenged the call at first base, but they were denied, ending the game.
—Field Level Media