NEW YORK -- If the Mets turn to Kodai Senga in relief on Friday, they won’t know exactly what to expect. But it’s entirely possible he will be part of the proceedings.

Senga, who was once in play to start National League Championship Series Game 5 despite his issues in Game 1 on Sunday, is now a candidate to come out of the bullpen for the first time as a Major Leaguer. The Mets chose to start David Peterson in a must-win Game 5 over Senga after managing to avoid using the left-hander in relief during Games 3 and 4.

“Facing an elimination game, he’s fully rested,” manager Carlos Mendoza said of Peterson. “He's been one of our starters, one of our best starters. We just feel like he’s going to give us the best chance.”

Although Peterson hasn’t delivered a full starter’s workload since September and is unlikely to do so in a potential elimination game, the Mets have enough well-rested relievers that they would probably only turn to Senga in a lopsided game. If they do, team officials have confidence that Senga can deliver a more competitive outing than he did in NLCS Game 1, when he threw 20 of his 30 pitches outside the strike zone, walked four batters and threw a wild pitch.

Senga threw a bullpen session Wednesday and looked significantly improved, according to a team decision-maker, which should bolster the Mets’ confidence in him. He also stretched out in the bullpen following his NLCS Game 1 start, which means an effective Senga could throw as many as four innings and approximately 60 pitches out of the bullpen in Game 5.

“He’s an ace, man,” Mendoza said earlier this week. “This is a guy that we saw making a start against the Braves [in July], and he was lights-out. He pitched against the Phillies [in the NLDS], and he was throwing 96, 97. It was one pitch that [Kyle] Schwarber got him, but other than that, he was pretty good. And then we’re reacting off one outing that he didn’t have it. So I’m pretty confident in giving him the ball.”

(While Tylor Megill was also once an option to start Game 5, his three-inning appearance in Game 3's 8-0 loss on Wednesday took him out of play for a bulk assignment Friday.)

Senga was the Mets’ best pitcher last season, producing a 2.98 ERA over 29 starts. And he was effective in two of his three outings this season, including a July 26 start against the Braves and an NLDS Game 1 start against the Phillies. Only in NLCS Game 1 did Senga struggle, explaining afterward that his mechanics were out of whack.

“He knows himself better than anybody,” Mendoza said. “At times, if something’s off, you’re going to see games like that. But if he’s right, he can be lights-out.”

Although one bullpen session represents a microscopic sample size, the Mets don’t have many other data points to evaluate Senga, who missed nearly the entire regular season due to shoulder, triceps and calf injuries. It wasn’t until early October that Mets officials began seriously considering Senga as an option for their playoff roster.

A week and a half into that experiment, they’re no more certain of what Senga can provide them. Peterson represents a lower-variance option, which is a significant reason why he’s starting Game 5.

“It means a lot,” Peterson said. “Being able to get the ball in a situation like this, and having the confidence of Mendy and the coaching staff is huge.”

Senga threw a bullpen session Wednesday and looked significantly improved, according to a team decision-maker, which should bolster the Mets’ confidence in him. He also stretched out in the bullpen following his NLCS Game 1 start, which means an effective Senga could throw as many as four innings and 60-ish pitches in Game 5.

“He knows himself better than anybody,” Mendoza said. “At times, if something’s off, you’re going to see games like that. But if he’s right, he can be lights-out.”

Although one bullpen session represents a microscopic sample size, the Mets don’t have many other data points to evaluate Senga, who missed nearly the entire regular season due to shoulder, triceps and calf injuries. It wasn’t until early October that Mets officials began seriously considering Senga as an option for their playoff roster.

A week and a half into that experiment, they may be no more certain of what Senga can provide them, but they’re still committed to chasing his upside.

“I never thought that he was going to be a player for us,” Mendoza said. “Now, because of where we’re at, you’re going to need somebody to start the game. He’s an ace. … That’s why there’s a chance he starts in Game 5.”