NEW YORK -- The Citi Field pregame routine took on an unusual air Monday, as a crowd gathered in the dugout shortly after 3 p.m. President of baseball operations David Stearns was there alongside a smattering of front-office officials. Manager Carlos Mendoza kept an eye on the proceedings, as did a group of relievers sitting on the outfield grass.

The main attraction was Kodai Senga, who was set to throw to live hitters for the first time since doctors diagnosed him with a torn posterior shoulder capsule in February. As the crowd of dozens watched from various vantage points, Senga threw 21 pitches to a group of Minor Leaguers brought in from Brooklyn for that express purpose.

“Nasty,” one of them said after facing Senga, who threw all his pitches and reached the mid-90s with his fastball.

Afterward, Senga, who has been tight-lipped about his timeline, said through an interpreter that he expects to return from the injured list “right around” the day he’s first eligible on May 27. Stearns later pushed back slightly on that timeline.

“It would be difficult for me to say with any accuracy whether it’s that last week of May or early June,” Stearns said.

The Mets have deliberately taken things slow with Senga in hopes that once he’s ready to return to the mound, his shoulder issue will never reoccur. Following his diagnosis, Senga went a full month without throwing a baseball. He subsequently spent five weeks playing catch off flat ground and throwing a series of bullpen sessions, before finally graduating to live BP on Monday.

Senga will face hitters two more times, with three days of rest between each session. If all goes well from that point, he’ll begin a Minor League rehab assignment around May 11. The right-hander will receive at least five days of rest following each Minor League start, so his ability to return by May 27 will depend upon whether he makes two or three-plus rehab outings.

Those are determinations the Mets will make in time. Monday, team officials were happy simply to see Senga in a competitive atmosphere once again. Mendoza, who trekked out to the bullpen to watch Senga warm up for his live BP session, came away impressed.

“The way the ball was coming out, there was no hesitation,” Mendoza said. “He was just letting it loose, using all of his pitches. Since he went down, the thing I’ve been saying is, ‘How is he going to bounce back?’ I think the biggest thing is tomorrow and the following day. But so far, he looked pretty sharp today."

Senga added: “Everything’s feeling solid. I think my rehab days have gone really well so far.”

The Mets’ best pitcher last summer, Senga produced a 2.98 ERA over 29 starts, with 202 strikeouts in 166 1/3 innings. He’s in the second season of a five-year, $90 million contract, which includes the ability to opt out after 2025 if he amasses at least 333 2/3 more innings before that time.