Pete Alonso lofted the walk-off sacrifice fly Monday night for the New York Mets, who edged the Pittsburgh Pirates 4-3 in the opener of a three-game series.

David Bednar (0-4) struck out Luisangel Acuna to open the ninth before Francisco Lindor’s routine grounder behind second base skipped under the glove of shortstop Isiah Kiner-Falefa. Lindor went to third when Soto singled to right-center on the next pitch and scored easily on Alonso’s fly out to deep right.

The walk-off win was the fourth of the season for the Mets. Alonso collected the eighth walk-off RBI of his career.

Huascar Brazoban (2-0) earned the win despite blowing the save in the ninth, of the Pirates tied the score via a single, an error by Lindor and a bunt before Ke’Bryan Hayes had the game-tying RBI infield single.

Jeff McNeil laced an RBI double in the fourth for the Mets, who have won five of seven. Juan Soto tied the game with a run-scoring groundout in the seventh, one batter before Acuna scored from second on Alonso’s infield single.

Lindor and Mark Vientos had two hits each for the Mets.

Kiner-Falefa homered leading off the second for the Pirates, who fell to 2-2 under new manager Don Kelly. Pittsburgh took a short-lived lead when Bryan Reynolds legged out the back end of a potential double play ball in the seventh.

Hayes and Kiner-Falefa had two hits apiece.

Mets left-hander David Peterson gave up two runs on five hits and three walks while striking out seven over six-plus innings. Peterson, who pitched into the seventh for the first time this year, exited after issuing a leadoff walk to Jared Triolo.

Pirates starter Paul Skenes allowed one run on six hits and three walks while striking out six over six innings. He had just one 1-2-3 frame, but the Mets stranded six runners against the right-hander.