The Mets' Pete Alonso celebrates after hitting a two-run home...

The Mets' Pete Alonso celebrates after hitting a two-run home run during the seventh inning against the Braves on Thursday in Atlanta. Credit: AP/John Bazemore

ATLANTA — In Amed Rosario and Pete Alonso, the Mets have what they hope amounts to an organizational gold mine: two homegrown, pre-prime position players who can be penciled into the lineup for the next half-decade — at least.

Whether each player can turn flashes of major-league greatness — Rosario’s late last season and Alonso’s in recent weeks — into full-fledged stardom is a question that can be answered only with time.

But for at least one game, in a 6-3 win over the Braves on Thursday night, they played like the franchise cornerstones the Mets think they can be. Rosario drove in a career-high four runs, Alonso added two RBIs, and each homered and had two hits as the Mets moved to 8-4.

“They are going to be cornerstones,” manager Mickey Callaway said. “If you’re going to win a World Series, if you’re going to make the playoffs, your young players have to perform, because you can’t go out and fill every position every year. So it’s good to see these guys stepping up and getting some confidence so they can keep it going.”

Alonso’s latest gawk-worthy long ball came in the seventh, a two-run shot that went 454 feet, splashing into an elevated fountain above the centerfield wall.

The line drive came off Alonso’s bat at 118.3 mph, according to MLB’s Statcast tracking system. He called it “definitely the hardest ball I’ve hit in my life.” It was the second-hardest batted ball in the majors this season — behind only Giancarlo Stanton’s 120.6-mph single on Opening Day — and the hardest homer by anyone other than Stanton and Aaron Judge in five seasons of Statcast data.

“I gotta do a couple more push-ups,” Alonso cracked. “But that’s really cool. To be in the same category as those guys, it means a lot. They’re two of the most prolific power hitters in the game right now.

“To see it hit the water, like, wow. That’s cool. I kind of surprised myself, to be honest.”

Three of Rosario’s RBIs came on a homer to right-center in the second inning. His slow exit from the batter’s box suggested he knew it was gone. In the seventh, he poked an outside slider from Wes Parsons into right for a two-out RBI single. That was the last run charged to Kevin Gausman (four runs, 5 2⁄3 innings).

Callaway said the Mets have been preaching to Rosario to hit balls back up the middle, especially in scenarios in which all the team needs is a base hit. With the homer, Rosario provided a bit more than that.

“He’s taking the good approach, staying back through the middle of the field,” Callaway said. “He’s not only listening but he’s able to go out there and implement it, and that’s a great thing to see.”

Steven Matz settled in after an iffy couple of innings to hold the Braves (7-5) to two runs in six innings. He retired 13 consecutive batters, including eight via strikeout, from the second into the sixth. Matz has a 1.65 ERA in three starts.

Altogether, it meant a successful start to the Mets’ season series with the Braves, which Callaway stressed Thursday afternoon as an important part of his team’s year. Last year, the Mets went 6-13 against Atlanta, which won the NL East title with only 90 victories.

This season, in a bulked-up division in which the Phillies, Mets and Nationals made big offseason moves, it’s easy to forget that the Braves were better than all of them in 2018.

“They took care of us last year,” Callaway said. “We have to make sure that doesn’t happen again.”

Frazier nears return. Infielder Todd Frazier (strained left oblique) will rejoin the Mets “any day now,” Callaway said. He went 1-for-3 with two walks and two RBIs for advanced Class A St. Lucie on Thursday.

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