For the first time in nearly six weeks, Kodai Senga was on a mound and throwing hard.

The first glimpse at a possible late-season weapon — however utilized — took form on Wednesday, when the right-hander threw 25 pitches in a bullpen session and looked good, Carlos Mendoza reported.

“The way the ball was coming out [was encouraging],” the Mets manager said before finishing off a sweep of the Red Sox, 8-3, at Citi Field. “It was good to see him in full uni and actually letting it go. Good step today.”

The next step will be more bullpen sessions as Senga begins to stretch out after a high-grade calf strain knocked him from his lone outing of the season on July 26. There is not enough time in the regular season for Senga to become a six- or seven-inning option for the stretch run.

There is enough time for Senga to take down three or four innings at the beginning of a game, a possibility president of baseball operations David Stearns hinted at this week.

“I think step one is: Let’s get him on a mound and to a place where we feel like he’s healthy enough to compete at the major league level,” Stearns said, “and then we’ll tackle the role — whether it’s bullpen, whether it’s starter, whether it’s a couple of innings at the front of the game.”

Senga has said he believes he will be able to help the team as soon as he is eligible to be activated from the 60-day injured list, which is Sept. 25.

On that date the Mets will be in the middle of what projects as their biggest series of the season, three games in Atlanta, and will have just five games left in the regular season.

As it stands now, the Mets have three trustworthy starting pitchers — Sean Manaea, Luis Severino and David Peterson — along with an up-and-down Jose Quintana, a returning Paul Blackburn and Tylor Megill, who has filled Blackburn’s spot in the rotation.

It is possible that in the final week of the season, the Mets could try Senga as a few-inning opener before, say, Blackburn takes over for the middle innings.

For now, Blackburn is expected to slot back into the rotation for a series in Toronto that begins Monday. The righty, who has been out with a right hand contusion, threw 6 ²/₃ innings of one-run ball with Triple-A Syracuse on Tuesday.

Blackburn has been excellent in three starts and knocked around in two since coming over at the trade deadline. He does not have the upside of Senga, who is trying to help at the tail end of what otherwise has been a lost season.

The 31-year-old, who finished seventh in NL Cy Young Award voting and second for NL Rookie of the Year last season, has dealt with setback after setback in Year 2 with the Mets.

First it was the right shoulder capsule strain, suffered in spring training, that ensured he would not be ready for the start of the season. Then came a series of complications in his rehab in which he did not feel comfortable with his mechanics and feared further injury, which delayed his season debut.

After four rehab outings, Senga returned to a major league mound on July 26, when he held the Braves to two runs in 5 ¹/₃ innings with nine strikeouts before attempting to chase a pop-up and going down in pain with an injury that initially appeared to end his season.

Following several weeks in which he could not stand and throw, Senga has begun building up — with a significant step arriving Wednesday.

The Mets want to find out how much he can help and in what role.

“If we’re making those [role] decisions,” Stearns said, “I’m really happy to be making those decisions.”

The front-office shake-up continued Wednesday, when longtime executive Ian Levin announced he is leaving the Mets after 20 seasons.

Levin, who had worked his way up to vice president and assistant general manager, will depart the organization at the end of the season.

Liz Benn, who as director of major league operations is the highest-ranking woman in the organization, also is leaving the club at the end of this campaign as part of an overhaul of the front office during Stearns’ first season as president of baseball operations.

Levin began as an intern with the Mets in 2005, worked in amateur scouting and analytics and ascended to farm director in 2015.

“I am confident that the Mets are poised for great things, and I look forward to watching the organization build towards its goals,” Levin said in an email announcing his exit.

In addition to front-office executives, there have also been several scouts who will not return to the organization.

“We have a very large scouting staff,” Stearns said last month. “We will continue to have a very large scouting staff.”

This offseason Stearns will have to fill out several positions and said Tuesday that he is not sure whether he will hire a general manager.

Megill lasted just four-plus innings in which he allowed three runs on five hits and a walk.

All the damage was done in the third inning, when three hits and two sacrifice flies plated three runs.

It is not clear whether Megill will receive another start.

He could be put in the bullpen.

“If that’s what they want me to do, then so be it,” Megill said of the bullpen. “I want to help this team win, and if that’s what I need to do, then that’s what I’ll do.”

The Mets have flip-flopped Sean Manaea and Jose Quintana in the rotation, with Manaea jumping in front to open a series against the Reds on Friday after an off day Thursday.

Quintana now will get the ball Saturday on two extra days’ rest.

Quintana has pitched better with more rest, which is part of the thought process.

What likely is also a factor is the late-season schedule: If the Mets use a six-man rotation the next time through the order then return to a five-man group, Manaea would line up to begin a series in Philadelphia and begin the series in Atlanta that looms as the largest of the year.

“Putting them in what we feel is the best position for them and for the team,” Mendoza said.

Mark Vientos (2-for-4 with a run scored) extended a 15-game home hitting streak in which he is batting .339. … Pete Alonso went 0-for-4 with three strikeouts and cracked his bat over his knee after swinging through a Kenley Jansen cutter in the eighth.

Jose Butto walked a pair in his second inning of work Tuesday and has allowed four runs and four walks in his past 4 ¹/₃ innings.

Mendoza said the righty had “a hard time recovering” on the club’s recent road trip and might have been fatigued in his first time working as a reliever rather than starter.

“But I think we’ve gotten through it,” Mendoza said. “He’s responded the past seven days or so, they’ve been a lot better.”

Tuesday, Mendoza said, “it got away a little bit.”

In a pregame ceremony, the Mets dedicated the Citi Field photo well to honor Marc Levine.

Levine, who had been the team photographer for about 3 ¹/₂ decades, died in July.