Francisco Alvarez got the green light and made it count.

With one swing from Alvarez, the Mets were rewarded for a solid night’s work against a tough opponent and got to celebrate on the base paths.

Alvarez’s first career walkoff homer gave the Mets a thrilling 4-3 victory over the Orioles at Citi Field for the perfect start to a 10-game stretch against top opponents.

Alvarez worked the count to 3-0 against Seranthony Dominguez with one out in the ninth before hitting a no-doubter to left-center.

The win was the Mets’ third in four games.  

David Peterson was on the verge of a gem before balking in a run and allowing a solo homer to Ramon Urias, both with two outs in the seventh.

Overall, the left-hander allowed three runs, two of which were earned, on six hits with eight strikeouts and one walk.

It was a fourth straight start in which Peterson – who leads Mets starting pitchers with a 3.00 ERA – has surrendered two earned runs or fewer in each of his last four starts.