Todd Frazier is more than a platoon player for the Mets these days, but certainly less than a starter.

That point became evident Monday, as the third baseman was on the bench for a second straight game against a right-handed pitcher. Jeff McNeil again started at third. McNeil has also played the outfield and second base.

Callaway was asked before the Mets beat the Diamondbacks 3-1 whether Frazier would start only against left-handers.

“Not necessarily,” Callaway said. “We just have to maximize people’s rest and there are going to be days he starts against righties and we have two lefties this series, he will definitely start both of those games. But it’s not just against lefties at this point.”

Frazier is 9-for-28 (.321) with two homers over his previous 10 games.

Callaway’s expectation is Brandon Nimmo and Juan Lagares will divide center field for the remainder of the season. Michael Conforto was in the center-field mix until recently, but team officials have liked Nimmo’s play enough since returning from the injured list.

“I think one of those will probably be in there every night,” Callaway said, referring to Nimmo and Lagares. “We’ll pick our spots for those guys, but we like those guys in center and they are kind of our center fielders and I think one of them will play every single night.”

Robert Gsellman is playing catch, but Callaway indicated it hasn’t been determined if the right-hander has a chance to return this season from a partially torn lat.

“We want to see how he bounces back every day and see what kind of progression we can give him,” Callaway said.

Gsellman has been on the injured list since Aug. 14.

Seth Lugo extended his scoreless streak to 13 innings and earned his eighth career save. The right-hander entered with the Mets leading 3-1 in the eighth inning and retired all six batters he faced. Lugo is tied with Milwaukee’s Josh Hader for the major league lead with 30 scoreless relief outings of two innings or more over the past two seasons.

With Jacob deGrom’s pitch count at 108 after retiring the Diamondbacks in the seventh, Lugo was expecting the extended duty.

“At one point his pitch count was kind of up there, so for a while I was hoping he would get through six,” Lugo said. “But he went out there in the seventh and did a real good job.”

Ketel Marte has emerged as a surprise MVP candidate. The Diamondbacks utilityman entered play Monday with a .330/.390/.599 slash line with 32 homers and 91 RBIs. Martel had a 1.132 OPS since June 14.

“[Marte] is short and quick to the ball,” Callaway said. “He’s always had that kind of compact swing. It’s hard to get in on him. You have to get way in there if you want to get it in there and he covers the plate and he’s got confidence because he is swinging the bat well this year. You could tell he was a good player in the past and he’s grown as a baseball player.”

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