NEW YORK -- Friday’s game had all the markings of another banner night for the Mets -- welcoming their ace back into the fold, celebrating the acquisition of a hard-throwing reliever, cruising to a fifth straight victory to move into second place in the NL East for the first time since March -- when one of the larger crowds at Citi Field all season suddenly went quiet.

As he moved off the mound to field an Austin Riley popup in the top of the sixth inning, Kodai Senga grimaced, grabbed his left lower leg and began hopping on his other one. Senga fell to the grass in pain as trainers and other staffers raced up from the dugout, surrounding him on the turf.

The injury wound up being a high-grade left calf strain for Senga, who walked off the field under his own power but, after an MRI on Saturday, he was placed on the 15-day IL and will likely miss the rest of the regular season. It was grim news for a Mets team that played the first 102 games of this season without their nominal ace, darkening what would have otherwise been an uplifting 8-4 win over the Braves.

“He’s a tough piece to lose,” said designated hitter J.D. Martinez, whose grand slam highlighted a seven-run third inning for the Mets. “But there’s no sense in dwelling on it. He’s going to do everything he can to come back, and hopefully he’s back by the playoffs. But there’s a lot of baseball left, so we’ve just got to keep it going.”

Until injuring his calf, Senga had been cruising through his first start of the season, after taking five months to recover from a strained posterior right shoulder capsule (and resulting complications). He allowed two runs over 5 1/3 innings in his debut, striking out nine batters and hitting 98 mph on the radar gun as the Mets built a six-run lead.

“You hate to see it, but look, he was pretty impressive,” manager Carlos Mendoza said. “Watching him pitch, the fastball, the command of his pitches, the splitter -- he dominated today. Yeah, you hate to see him go down like that, especially with what he’s been through the whole year. But people will step up.”

The question now becomes how much time Senga will miss. Like many soft-tissue injuries, recovery periods for calf strains can range from a week or two to multiple months, according to the Cleveland Clinic. The website Baseball Prospectus, which tracks injury recovery times, lists the average rehabilitation period for a calf strain at just under five weeks.

The good news for the Mets is that the club’s training staff has mostly ruled out a more severe injury, such as a ligament or tendon tear. Senga was unavailable to address the media after the game because he was receiving treatment.

"It's a high-grade strain," Mendoza said Saturday afternoon. "So, tough news obviously. Hard to put a timetable here, but I think it's fair to say that he's pretty much done for the regular season."

Despite his briefer-than-expected outing, Senga came away with a victory thanks to the seven-run third inning. Martinez hit a grand slam, while Mark Vientos and Francisco Alvarez also homered off Braves starter Charlie Morton. The win not only pushed the Mets past the Braves for second place in the division, but it also put them in the top NL Wild Card position -- a run up the standings that they accomplished almost entirely without Senga.

“It’s obviously a big piece, losing him,” Martinez said. “The way he threw the ball today was amazing, and it was exciting. Obviously, we hope he comes back as quick as he can. But I personally feel everyone’s like, ‘Next guy up.’ That’s what it’s been like all year for us.

“This is a team, a month ago, no one thought we were going to be here. We just want to keep the vibes positive and keep everything good and happy, and let’s just keep rolling.”