Mets third baseman Mark Vientos, left, and Red Sox first baseman...

Mets third baseman Mark Vientos, left, and Red Sox first baseman Triston Casas.

BOSTON — Mark Vientos, back for a third stint in the majors but seemingly in the same part-time role, has an ardent supporter in the opposing dugout this weekend: Red Sox first baseman Triston Casas, his best friend since they were 9.

Vientos and Casas grew up together as South Florida youth baseball hotshots. They eventually became high-end draft picks out of baseball powerhouse American Heritage School in Plantation — Vientos in the second round in 2017, Casas in the first round in 2018.

Now they are living the improbable childhood dream, reaching the majors late last season and — for this series — playing against each other.

Casas, a more highly regarded prospect, is getting his chance as Boston’s everyday option at first base and hit two home runs Saturday night against Max Scherzer. Vientos, who went 2-for-4 with an RBI single in the ninth, is still waiting for his.

“He’s put up numbers that merit a starting spot in the major leagues,” Casas said in an interview with Newsday. “I hope he gets a good opportunity to get some at-bats, because I know at every level in the minor leagues, he’s been able to succeed with a lot of at-bats. So I think once he gets his feet wet and once he settles his nerves at this level, especially playing in a city like New York — just as passionate as Boston — he’s going to be fine.”

Vientos has struggled to convert his minor-league success into major-league production. Entering play Saturday, he was batting .173 with a .259 slugging percentage in 90 sporadic plate appearances this year and last. Manager Buck Showalter made him the DH against Red Sox lefthander James Paxton on Saturday night.

Publicly, Vientos has said all the right things, downplaying the difficulty of getting into a rhythm when barely playing and trying to contribute whenever the Mets do put him in the lineup. Casas — a “brother” to Vientos, Vientos said — acknowledged that the playing-time dynamic has been rough.

 

“He’s frustrated because he’s been putting up really good numbers and not getting an opportunity, but he understands whether he’s in Triple-A or whether he’s in the major leagues, getting better that day is what his focus has been,” Casas said. “That’s what we’ve been talking to each other about.

“As a person, he’s selfless. He no matter what always puts other people before him. I think that mindset as a teammate is exactly what you want in that clubhouse. Hopefully he gets a chance to stick there long enough so everybody can jell to him.”

At the start of the series, on his first day back in the majors, Vientos was enthused about getting to play against Casas and creating a keepsake by taking a photo together on the field at Fenway Park — but only after a game in which Vientos played. He couldn’t make that memory with a completely clean uniform, he said.

When they were kids, Casas always was the more powerful hitter, Vientos said. Both played shortstop, and Vientos claimed the title of being the better pitcher of the two.

Casas, supportive of Vientos’ professional aspirations and most anything else he wants, scoffed.

“I don’t know when, because he stopped pitching in middle school. I still pitched in high school,” Casas said. “I know he used to be a good little pitcher like when we were in 10U, but I was the closer of our team [in high school]. I don’t know what he’s referring to, better pitcher.”

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