Francisco Lindor and Pete Alonso hit solo homers for the Mets (64-74), who have won four of their past five games. Alonso has 42 home runs this year, while Nimmo went 3-for-5 and scored three runs from the leadoff spot.
Jose Quintana pitched seven strong innings for the win, though his efforts were overshadowed by New York's power display. Quintana (2-5) gave up one run, four hits and one walk while striking out four.
Washington (62-77) has lost six games in a row, so it will spend more time in the National League East cellar. The teams meet in the final game of the two-game set Wednesday night.
Joey Meneses' single in the first inning drove in the Nationals' only run until they plated four in the eighth.
Nimmo belted solo shots in the fourth and ninth innings, giving him 22 home runs this year. It marked his second two-homer game of the season.
Alonso began the scoring with a sacrifice fly in the first before Alvarez hit his 22nd long ball later in the inning. Lindor's 26th blast came in the third, and Alonso went deep in the fifth to boost the lead to 9-1. Alvarez wound up scoring three runs.
Patrick Corbin (9-13) took the loss, allowing eight runs on seven hits and a walk in four innings. He struck out two. Washington relievers Andres Machado and Amos Willingham each gave one homer.
Brett Baty drove in two runs for the Mets, who had a total of 11 hits. New York batters struck out only three times.
Jacob Young went 2-for-4 with a walk and two runs, finishing as the only Washington batter with more than one hit.
—Field Level Media