The Mets (63-74) won a series for just the fourth time since Aug. 1. The Mariners (77-59), who led Houston by a half-game in the AL West before the Astros' game Sunday night, lost for the fourth time in 18 games.
Alonso has 41 homers and 100 RBIs — the third time he's hit at least 40 homers and racked up at least 100 RBIs in five big-league seasons.
Francisco Alvarez laced a run-scoring RBI single in the second while Jeff McNeil homered leading off the fifth. McNeil and Brandon Nimmo had two hits apiece.
Tylor Megill (8-7) gave up three runs on five hits and two walks while striking out six over 5 1/3 innings. Adam Ottavino, the Mets' fourth pitcher, notched his eighth save with a one-hit ninth. He struck out three.
The Mariners' Dominic Canzone and Mike Ford homered in the fourth.
Starter George Kirby (10-9) allowed four runs (three earned) on six hits and no walks while striking out three over three innings.
The Mets scored an unearned run in the first, when Lindor reached on a one-out error by second baseman Josh Rojas before scoring from first on Alonso's two-out single.
McNeil led off the third with a single and Alonso followed with his milestone homer.
The Mariners got just one runner beyond first base over the first three innings before mounting a two-out rally in the fourth. Megill plunked Eugenio Suarez, after which Canzone and Ford hit consecutive homers.
McNeil opened the fifth inning with his seventh homer and Alonso homered for his 100th RBI of the season with one out in the seventh. He has five multi-homer games this year, including four since July 25.
—Field Level Media