NEW YORK -- Usually, when a player hits a dramatic go-ahead home run in a late inning at home like Todd Frazier did for the Mets in Thursday’s 7-3 victory over the Giants, the cheers from the crowd are immediate. But this one was different.

Everyone on the field and in the stands seemed to pause, uncertain whether the ball was going to leave the park. Even the pitcher who allowed it, Mark Melancon, didn’t have the normal disappointed reaction to giving up a home run. Instead, with a runner on second and one out, Melancon ran to back up the throw home in case the ball got in the gap.

But it never landed in the park; it was a tiebreaking home run that put the Mets up 5-3 for a lead they would not relinquish.

• Box score

It’s easy to see why the consensus reaction occurred, though, given that the ball had a 94.7 mph exit velocity -- not even a hard-hit ball -- and Frazier swung with his right knee practically touching the ground and his top hand letting go of the bat.

“Anytime … they take a swing, out on their front leg and almost their back knee on the ground, you don’t anticipate that it’s going out," manager Mickey Callaway said. "You usually read the swing. And then it just kept on going.”

The one person who knew it was going out the whole time? The batter himself, Frazier.

“I had an inkling it was [going] out," he said. "I’ve done that a couple times in my career, just one of those things where I actually squared it up, as silly as that sounds.”

Callaway also noted that Frazier has had a proclivity for such home runs in the past.

“It looked like Frazier knew it was gone,” Callaway said. “You know he’s hit so many of them like that. So he was aware that it was gone, but we were like, ‘Get in the gap, get in the gap!’ and then it goes over the fence.”

Both sides were shocked the ball carried out.

"He golfed it out,” San Francisco manager Bruce Bochy said. “He can do that on that low pitch. He is a pretty good hitter. It carried out. I thought it was a fly ball. I was surprised how far it went. He is strong.”

The numbers back up the improbability and uncertainty, too. Frazier’s homer had a .230 expected batting average, based on its exit velocity and launch angle. The Mets have hit just three home runs this season with a lower expected batting average, and two of those were also homers to left at Citi Field -- one of which Frazier hit, a grand slam on April 23.

So how did Frazier do it?

“You’ve gotta get underneath it," he said. "The back leg has to get really down. … I know Adrian Beltre used to do that really well. [He] used to get his back knee down low, so I kind of did that and found a way to get my bottom hand underneath it.

“You have more time on a curveball, so just one of those things where I do have that kind of swing sometimes and … I’m either going to foul it off or miss it wildly. Just one of those times where I found a way to get a good piece on it.”

One more element of improbability, in Frazier’s eyes, was the pitcher off whom he hit it.

“I feel like I’ve gotten one hit off him in like 30 tries, so I’ll take it," Frazier said of Melancon. "He’s a really good pitcher, and we just had his number today.”

Frazier undersold himself a bit. He entered Thursday's game 3-for-13 in his career against Melancon, but each of the three hits had been singles.

Frazier finally got his first extra-base hit off the Giants right-hander to start an eighth-inning rally, even though almost nobody but Frazier knew it would be a home run until it landed beyond the wall.