The clubhouse door swung open and in strode Robinson Cano and Amed Rosario.

Together — as usual.

The veteran and the youngster aren’t next to one another in the field lately because Cano is attempting to return from a torn left hamstring, but that hasn’t changed the dynamic between the two.

When there is downtime, they are often side by side. It can be in the clubhouse. It can be in the dugout. But when you see Cano, you usually see Rosario right there, listening to advice from the eight-time All-Star.

“They’re together constantly,” manager Mickey Callaway said.

It’s not a stretch to say Cano, 36, has at least helped Rosario break out and become an impact player in the second half of the season, keying the Mets’ furious surge into wild-card contention. The two have been attached at the hip since spring training, quickly developing a close bond. Cano helped Rosario deal with his early struggles and stressed to him the importance of plate discipline and consistency at-bat to at-bat.

“This year I have to be really grateful for him,” Rosario said through an interpreter, before a miserable 0-for-6 outing Friday night in a 2-1 loss in 14 innings to the Braves at Citi Field. “Throughout the whole year, he’s been helping me a lot. Both physically in how I work and mentally how I prepare myself. He’s been a veteran in the game. He’s seen a lot.

“It was just the chemistry right away. We just have good chemistry the way we get along,” added the 23-year-old Rosario, who entered Friday fifth in the National League in batting (.362) and second in hits (54) since the All-Star break, and who has reached base safely in 33 of his past 36 starts. “I like to learn from older players, because I know they have a lot to teach.”

That’s not to say others shouldn’t be recognized, too. Rosario is the one producing. Hitting coach Chili Davis, Cano pointed out, works with Rosario on a daily basis in the cage.

Callaway shouldn’t be forgotten, either, for continuing to express confidence for his player, both publicly and privately. But having someone with the experience and success of Cano in his corner has surely helped, too.

“It’s great when you have someone like that being able to teach you,” Rosario said.

The results are clear. Rosario is now looking like the player most predicted would be an All-Star when he was an elite prospect, rather than the inconsistent young player who frustrated fans.

“He’s just maturing,” Cano said. “Sometimes as a young player you think you can hit everything. You think everything is going to be a strike.”

Cano said they talk a lot about plate discipline, which he stressed to Rosario was the key for the young shortstop to take his game to the next level.

Lately, Rosario has made significant progress in that area. He has cut down on his strikeouts and chases pitches out of the strike zone less often. Rosario is seeing the results.

“He can be one of the best shortstops in this game and I guarantee you he will be,” Cano said.

Rosario was thrilled to hear such a compliment. But he also said his recent success, and the plaudits that have come with it, wouldn’t impact him negatively.

“That makes me work even harder,” Rosario promised, “when a superstar like Robby says I can be as good as he thinks I can be.”