The Mets had to think rookie slugger Pete Alonso was pretty gassed to take him out of the lineup Friday night against one of the top left-handed starters in baseball, Clayton Kershaw of the Dodgers.

“He’s totally fine. We just all felt like he needed an off-day,” Callaway said about not starting Alonso, who pinch-hit for Juan Lagares in the seventh inning of the Mets’ 9-2 loss to the Dodgers and stayed in the game at first. “Talking to everybody, just seeing Pete for the last few days, I think an off-day’s warranted for him.

“I think he’s played more games than any rookie, more games than most players. It’s been a lot of games in a row for him. So off, for some of the game, at least.”

Callaway believed Alonso’s pitch selection in Thursday’s series-sweeping win over Arizona indicated that he was “fatigued” and needed a break, but the Mets’ manager expects his Rookie of the Year front-runner to start the remaining 15 games of the team’s playoff push beginning Saturday.

“No, this is his day,” Callaway said of Alonso, who gave the Mets a small boost by walking twice. “He’s got to play. He’s our guy. He’s what makes us tick. He’s our energy drink.

“We’ve been leaning on this guy for the whole season. He’s carried us for most of the season. Now we’ve got a bunch of guys performing well. We can afford to give him a day off, so let’s do it. Let’s get Pete back the way he needs to be.”

Todd Hundley, who shared the previous Mets mark for home runs in a season with Carlos Beltran, was at Friday’s game and chatted with Alonso after batting practice. Hundley hit 41 home runs for the Mets in 1996.

“No matter what year you’re in, that many home runs is tough to do, rookie or in your 20th year,” Hundley said. “It’s awesome. It’s a lot of home runs, and obviously he’s still going. It looks a lot easier than it is, to be honest with you. He’s just an all-around good hitter.”

Todd Frazier started at first base for Alonso, only his second start there this season. Frazier, who went 1-for-4, moved to third when Alonso was subbed for Lagares.

“He obviously can catch a groundball with the best of ’em. And he understands the game probably more than any player I’ve been around, in terms of situations, where people need to be on cutoffs,” Callaway said of Frazier. “He is totally comfortable over there, and he had a pretty big smile on his face when I told him he’d be playing first.”

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