Yarbrough (1-3) followed opener John Curtiss in the second inning and gave up one run and five hits over 5 2/3 innings for his first win since Aug 11, 2019 at Seattle.
''Really happy for Yarbs,'' Rays manager Kevin Cash said.
Nick Anderson replaced Ryan Sherriff with the bases loaded and one out in the ninth and struck out Luis Garcia and pinch-hitter Yadiel Hernandez to get this fifth save.
The Rays are 3-4 in a stretch of eight straight games against last place teams.
Washington got a sixth-inning RBI grounder from Kurt Suzuki.
Yarbrough's skid consisted of all starts. The lefty has had success coming out of the bullpen, going 23-5 in 47 career relief appearances, many following an opener.
''Really attacking guys,'' Yarbrough said. ''Got the breaking ball going, kept guys off balance.''
Manuel Margot chased Anibal Sanchez (2-5) with a bases-loaded, one-out RBI infield single in the fifth that put the Rays up 3-0.
''Definitely, I would love to pitch better, get a better result for myself and for the team and finish the way that I want,'' Sanchez said. ''I think this year, I feel healthy all the way through the whole short season, and I think right now if we had a regular season, my body, it feels good.''
Tampa Bay added three more runs in the fifth against Ben Braymer, who walked Lowe with the bases loaded and gave up Kevin Kiermaier's two-run single.
Kiermaier had missed the previous two games due to general body soreness.
Lowe homered and Kevan Smith had an RBI single as the Rays went up 2-0 in the second.
''I think we did a good job of capitalizing when the opportunity presented itself,'' Tampa Bay infielder Mike Brosseau said. ''Going down to the wire here, we're looking to capitalize as much as we can.''
Sanchez allowed six runs and seven hits in 4 1/3 innings. He also had a balk and the Rays stole four bases against him
''He's so focused on just getting outs at home plate that his times are just not good,'' Nationals manager Dave Martinez said. ''With a team like that we know coming in, the conversation before games is, `Hey, you've got to be able to hold runners on, because they're just going to run.' He didn't do that tonight.''
Washington's Juan Soto was 1 for 4 with a double. Since returning to the lineup on Sept. 8 following a stint on the injured list, Soto is 6 for 18 and has reached base safely in 16 of 28 plate appearances.
Nationals: RHP Tanner Rainey (right flexor strain) was placed on the 10-day IL. ... INF Brock Holt went on the paternity list.
Rays: RHP Oliver Drake (right biceps tendinitis) was reinstated from the 10-day IL. ... 1B Ji-Man Choi (left hamstring strain) went on the 10-day IL. ... C Mike Zunino (left oblique strain) is taking live at-bats at the alternate training site.
Nationals RHP Austin Voth (0-5) will start the series finale on Wednesday. RHP Pete Fairbanks (4-3) will be an opener for Tampa Bay.
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