Austin Barnes, Jason Heyward and Freddie Freeman all notched two hits apiece for Los Angeles, while Freeman and Max Muncy both scored two runs.
The Dodgers (87-55) completed a 3-3 road trip that began in Miami.
The Nationals (64-79) concluded a nine-game homestand by going 2-7. Rookie Jacob Young and Ildemaro Vargas both had two hits for Washington, which totaled nine — all singles.
Rain interrupted this game, as it did in the first two games. This one came with Los Angeles up 5-2 and the bases loaded with one out in the top of the fifth inning. The series included about seven hours' worth of delays.
Ryan Yarbrough gave the Dodgers a solid start on the mound, but he didn't return after the delay. In four innings, he gave up two runs on five hits without a walk and struck out five.
Wander Suero (1-0) was the winning pitcher despite giving up one run in 1 1/3 innings.
Nationals starter Trevor Williams (6-10) had another rough start, surrendering six runs on eight hits in 4 1/3 innings. He walked four and fanned four.
Heyward had a two-run single in the first inning. Outman's 19th homer of the season led off the second. Later in the inning, David Peralta was hit by a pitch with the bases loaded to make it 4-0.
Washington scored when rookie catcher Drew Millas singled home two runs in the fourth inning.
The Dodgers added two runs in the fifth on Rojas' single and Barnes' sacrifice fly. Enrique Hernandez doubled in Freeman in the sixth.
The Nationals had the potential for a big inning in the sixth by loading the bases with one out. Jake Alu struck out, but Young's infield single scored one run. Lane Thomas popped out to end the inning.
—Field Level Media