Carter Kieboom capped a two-run rally in the bottom of the ninth inning with a walk-off single as the host Washington Nationals stunned the playoff-contending New York Mets 4-3 in the finale of a five-game series.

The loss was costly for New York (69-69), dropping it four games behind the idle National League East-leading Atlanta Braves (72-64) with the Mets having 24 games remaining, including a three-game set on the Braves' home field on the final three days of the regular season.

Seeking his 29th save with a 3-2 lead, Mets closer Edwin Diaz (5-5) sandwiched a Juan Soto foulout with walks to Alcides Escobar and Josh Bell to open the ninth.

Pinch-hitter Andrew Stevenson tied the game with a single to right field, scoring Escobar and sending Bell to third, from where he jogged home on Kieboom's game-winner to center.

The walk-off win was the Nationals' seventh of the season, two of which have come against the Mets.

After the clubs had exchanged single runs in the first and fourth innings, Pete Alonso belted Patrick Corbin's second pitch of the sixth over the wall in left field for his 30th homer of the season and a 3-2 lead.

New York retained that lead until the bottom of the ninth before Diaz was rocked for his second blown save of the series.

Kyle Finnegan (5-6), who pitched two scoreless innings in relief of Corbin, was credited with the win.

Alonso opened the Mets' scoring with an RBI single in the first inning, scoring Francisco Lindor, who had doubled.

Javier Baez, who had singled, scored New York's fourth-inning run on a double play grounder by Jeff McNeil.

In winning for just the 17th time in their last 59 games, the Nationals matched each of the Mets' first two scores with a Soto run-scoring infield out in the first and a Lane Thomas RBI single in the fourth.

Corbin went seven innings, allowing all three Mets runs on 11 hits. He walked one and struck out four.

Washington scored its first two runs against New York starter Trevor Williams, who worked the first five innings. He allowed 10 hits and two walks, striking out three.

Luis Garcia had a triple and a single and Alex Avila a double and a single for Washington, which completed a 2-6 homestand. Kieboom and Thomas added two singles apiece.

Alonso, Lindor, Baez and Kevin Pillar had two hits each for the Mets, who nonetheless won the season series from the Nationals 11-8.

--Field Level Media