Mets starting pitcher David Peterson delivers against the Marlins during...

Mets starting pitcher David Peterson delivers against the Marlins during the first inning of an MLB game at Citi Field on Saturday. Credit: Kathleen Malone-Van Dyke

David Peterson saw an opportunity and grabbed it. With Marcus Stroman sidelined by a torn left calf muscle, the rookie lefthander has assumed a spot in the Mets’ starting rotation and performed very well.

In the Mets’ 8-4 win over Miami on Saturday night at Citi Field, he allowed two runs in five innings and improved to 2-1 with a 3.78 ERA. His fastball sat around 93 mph and his slider was effective as he pitched deeper into the game. Twice he stranded a Marlin in scoring position.

“With every start, I feel I get more comfortable here. I learn more . . . I’ve gotten a good taste in three starts and I’m trying to work off the successes that I’ve had,” said Peterson, the Mets’ first-round pick in the 2017 draft. “I’ve been up here for a reason and that gives me confidence to get out of any jam and I take that into my starts.”

“He looks like a polished pitcher,” Michael Conforto said.

Stroman threw 80-plus pitches in a simulated game on Thursday and will throw another no earlier than Tuesday. Mets manager Luis Rojas said the former Patchogue-Medford star is pitching effectively and healing well but still isn’t able to field his position because of the calf. The very soonest he could return is next weekend, and that is not assured.

Rojas said that when Stroman returns, “we want him to finish the season.” In the meantime, Peterson will try to make it a hard decision.

“He’s a competitor, he wants the ball and he wants to attack you,” Rojas said. “He’s been giving us what we want from a starter.”

“He’s a competitor, he wants the ball and he wants to attack you,” Rojas said. “He’s been giving us what we want from a starter.”

Infield chemistry

he Mets have a pair of blossoming young infielders in starting shortstop Amed Rosario and utility infielder Andres Gimenez. It’s not a stretch to envision them starting together in seasons ahead.

The duo has started twice together on the left side of the infield and once on either side of second base. Brian Dozier started at second Saturday night and Gimenez was a defensive replacement in the eighth.

“It’s a pleasure to play alongside him,” Rosario said of Gimenez on Saturday through an interpreter. “He’s a talent that you can’t hide. It’s super-obvious how talented he is.”

Gimenez, a rookie, came up as a shortstop but has played second and third base with Rosario firmly installed at short. When Rosario had a day off, Gimenez started at short.

There will be plenty of time for the relationship to grow, and Rosario said it has been easy working with him in the infield.

“I don’t know if (people) have realized, but he’s a super-intelligent player,” Rosario said. “He pays attention to the little details, which is always big in the team aspect. But he always brings a lot of energy.”

Davis taking to third

The Mets started Jeff McNeil in leftfield and J.D. Davis at third base for the second straight game Saturday. The previous six times both started, it was the other way around — Davis in left and McNeil at third — but this might be the new paradigm.

Davis hit a three-run homer in the seventh Saturday night to give the Mets a four-run cushion in their 8-4 victory.

Davis is a much better third baseman than outfielder — he had some awkward moments in leftfield the first week — and McNeil is the more experienced outfielder. Davis made a pair of excellent defensive plays this past week, and his strong arm has made an impression.