With six starting pitchers and only five rotation spots, the Mets have shifted rookie David Peterson to the bullpen.

Manager Luis Rojas framed it as a temporary move, and Peterson helped immediately with four shutout innings in Wednesday's 9-4 win over the Orioles. But the Mets appear committed to stretching out Robert Gsellman and Seth Lugo as starters, and they have built the rest of their rotation around three pitchers under guaranteed contract: Jacob deGrom, Rick Porcello and Michael Wacha.

Gsellman will start Thursday against the Yankees at Citi Field.

“Moving forward, we’ll definitely address where [Peterson] is at, if he’s starting a particular game the next time around,” Rojas said. “But as of today, this game, he’s ready to come out of the 'pen.”

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Barring injury, the Mets do not have an obvious rotation opening, but injuries do happen. So do doubleheaders, which would provide another route for Peterson to return to starting games. The Mets have also received inconsistent performances from Wacha and Porcello, and could consider making performance-based changes in the future.

For now, though, Peterson is a reliever, capable of throwing 70-plus pitches out of the bullpen if needed. He fired 59 in Baltimore, giving the Mets length after Wacha lasted only three innings.

“Right now, we have six guys that they’re stretched out to a point,” Rojas said. “One of the things that we’re doing with keeping Peterson there is because he’s going to give us the length that we need. Length should protect our bullpen on a day like this, if we need it. And at the same time, Peterson’s a guy that’s thrown the ball really well for us, so he’s going to be out there and he’s going to be competing real well. He’s going to put us in a good position to win games.”

Rojas added that the decision had nothing to do with the Mets protecting Peterson, who spent time on the injured list earlier this month battling left shoulder fatigue. It was simply a function of the roster.

Added to the rotation shortly after Opening Day because of injuries elsewhere, Peterson went 3-1 with a 2.91 ERA in four starts before landing on the IL. But he allowed three runs in four innings on Friday at Yankee Stadium in his return.

Back (and batting cleanup)
Two days after the Mets acquired him for a player to be named later, Todd Frazier reported to a familiar clubhouse, filled with many of the same players who were there last season. Rojas immediately slotted Frazier in at cleanup, starting him at third base.

“I’m not stepping on anybody’s toes,” Frazier said, noting that the Mets never pursued him in free agency last winter after he spent two seasons with the club. “I’m just going to be myself, like I’ve always been.”

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Frazier should mostly come off the bench against right-handed pitchers, but he was in the lineup Wednesday because the Mets were facing Orioles lefty John Means. That made him a better option in Rojas’ eyes than lefty hitters Luis Guillorme or Andrés Giménez, one of whom would have started had Frazier not been an option.

Frazier featured extreme platoon splits over 31 games with the Rangers, batting .192/.272/.315 against right-handed pitchers and .343/.425/.514 versus lefties. On Wednesday, he went 0-for-5 with a strikeout but made a great play on his first defensive opportunity.

Gang’s all here
In addition to Frazier, trade acquisitions Robinson Chirinos and Miguel Castro also reported for duty on Wednesday. To clear roster space, the Mets optioned pitchers Ariel Jurado and Franklyn Kilome to their alternate site in Brooklyn, along with catcher Ali Sánchez.

Chirinos spent his first day becoming acquainted with Mets pitchers, soaking up as much as possible from the Mets’ starting backstop, fellow Venezuelan Wilson Ramos. The two have played against each other for years, both in the Majors and the Venezuelan Winter League, but do not know each other well, according to Chirinos.

“I’ve been talking to Wilson today, and just doing my best to pick his brain,” Chirinos said of Ramos, who is not in danger of losing his starting job. “He’s been here the last couple years. He knows pretty much everybody. He’s been open-minded to me. He’s been sharing information with me, and I appreciate him for doing that.”

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Castro made his debut on Wednesday and needed just 11 pitches for a clean eighth inning against his former team.

“It was weird, because it was the last thing I was expecting,” Castro said. “One moment you’re with a team, and the next they’re calling you telling you that you’re traded.”

From the trainer’s room
Third baseman J.D. Davis was back in the Mets’ lineup on Wednesday, albeit at designated hitter after missing two days due to a sore left hip, going 2-for-3 with a walk. Davis had been hurting since taking a 99-mph fastball off his hip during Saturday’s loss to the Yankees. He pinch-hit in Tuesday's loss to Baltimore.