Mets shortstop Amed Rosario rounds third base on his grand...

Mets shortstop Amed Rosario rounds third base on his grand slam against the Miami Marlins during the first inning at Citi Field on Friday. Credit: Kathleen Malone-Van Dyke

Mickey Callaway was enjoying the Mets’ blowout win over the Marlins on Friday night when something unusual happened: Amed Rosario walked.

In addition to being a rarity in itself, it meant the shortstop had reached base twice in the same game.

That came shortly after Rosario had two hits on the same day in San Diego, which was preceded by three hits in a game in Milwaukee.

Rosario’s offensive numbers aren’t exactly imposing — he is hitting .278 with a .316 on-base percentage and a .424 slugging percentage — and he still lags well behind the top couple of tiers of offensive shortstops so prevalent in the modern major-league world. But each component of his slash line is a career high, and the Mets are encouraged by his progress.

To hear Callaway tell it, it has taken until about now for Rosario, 23, to treat each at-bat equally. He’s figured out that getting on base more than once is better than getting on base once.

“The funny thing about Rosario is he stays in the .260-.270 range, and you don’t see tons of games where he gets multiple hits,” the manager said. “It’s like he gets one a night, one a night, one a night. And then lately we’ve been seeing him break out and getting a little bit more of those multiple-hit games, which is very encouraging.

“It’s nice to see that consistent performer that’s getting that one on-base or one hit a night, but to start realizing that he’s capable of a little bit more and he can get on base twice, and that’s not bad. That’s fun to see. That just tells me he’s maturing, he understands that you know what, I can go up there every at-bat and grind away.”

Rosario leads the National League with 10 errors, all during a 17-game stretch, but has shown signs that he is beginning to stabilize defensively, including a couple of recent diving stops deep in the hole followed by strong throws to first.

If he could avoid making regular misplays, it would allow observers to notice his bat more often. Rosario has hit in seven straight games and 21 of his past 23 spanning a month. His total of 24 RBIs ranks sixth among shortstops, and he leads the Mets in batting with runners in scoring position at 14-for-39 (.359). That’s better than Jeff McNeil (.333), Wilson Ramos (.325), Robinson Cano (.273) and Pete Alonso (.267).

The recent production has come as Rosario has moved all around the lineup. This month, he has batted second (three times), sixth (once), seventh (twice) and eighth (three times).

Callaway pointed to that Friday game as evidence of Rosario’s growth. After a first-inning grand slam, he struck out on three pitches — including a whiff on a curveball in the dirt — in the second inning against the same pitcher, Miami’s Pablo Lopez.

“He didn’t look quite locked in,” Callaway said. “That’s still just a young kid trying to get through a season.”

But later, a walk.

“He’s slowly understanding what it takes to hit is to grind out every single at-bat and give yourself the best chance to continue to get on base,” Callaway said. “Even if you got on base your first time, you’re going to have three more at-bats. Go get on base the second time. Go get on base the third time. I think he’s really starting to understand that. We’ve seen more success lately because of that.”