NEW YORK -- For the surging Mets, a four-game series against the reigning National League West-champion Giants offered a significant early-season test. So far, they have passed. Francisco Lindor hit a walk-off single in the 10th inning of Game 1 of a doubleheader on Tuesday to give the Mets a 5-4 win and the second-best record (8-3) in baseball.

The Mets nearly gave up the go-ahead run in the top of the 10th, but in a key reviewed play, Pete Alonso kept his foot on the first-base bag to corral an errant Lindor throw. That ended the half-inning, giving the Mets a chance to walk things off. With runners on the corners and one out against Jarlin García, Lindor slashed a single back up the middle, plating Brandon Nimmo with the winning run.

“[Lindor] seems to be dealing up what we need every time,” manager Buck Showalter said.

For the first time this season, Mets starter Tylor Megill appeared mortal, allowing four runs over the first three innings as his peak fastball velocity dipped into the mid-90s. But he recovered to end his afternoon with three consecutive scoreless innings, ensuring that the Mets’ multiple late rallies would matter.

“Obviously, things didn’t get off to a hot start, but I settled in nicely toward the end,” Megill said. “That’s what it’s all about, the team just grinding at-bats. … Look what happened. We came back and we won.”

The first of those rallies occurred in the fifth inning, when Travis Jankowski beat out a potential double-play ball to keep pressure on Giants starter Alex Cobb. James McCann, Jeff McNeil and Lindor all followed with two-base hits to tie the game.