CHICAGO — Edwin Diaz’s already dramatic season took another turn Sunday night.

As Diaz entered for the bottom of the ninth inning in the Mets’ 5-2 win over the Cubs, crew chief Vic Carapazza ejected him before he ever threw a pitch when a routine check of his hands and glove yielded — in the umpire’s view — the discovery of an illegal substance.

Drew Smith (two outs) and Jake Diekman (one out) handled that final frame, but at almost the last moment, the story became something other than the Mets’ ninth win in 11 games.

Under the norms established by MLB since 2021, when it began enforcing its longstanding policy on doctoring baseballs, any sticky-stuff ejection comes with a 10-game suspension. The league is expected to announce that punishment for Diaz on Monday. He’ll be scheduled to sit out through July 5.

“As soon as they saw me, they were trying to throw me out of the game,” said Diaz, who added that he was “really surprised” by Carapazza’s reaction. “I understood. That’s their job. That’s part of the game. When they threw me out of the game, I just kept walking to the dugout.”

Diaz repeatedly insisted after the game that he was using rosin, sweat and dirt, same as always. He also said the coloring of his hands and the amount of those substances on his hands were in line with his standard.

Carapazza disagreed, telling a pool reporter that “it definitely wasn’t rosin and sweat.”

He added: “The substance was extremely sticky. Discolored. That was that. We’ve checked thousands of these. I know what that feeling is. This was very sticky.”

Diaz added: “I said, you can check my hand, smell my hand. It doesn’t smell like anything. But they threw me out of the game.”

Diaz said he won’t change his pre-appearance routine as a result of this episode.

The Mets didn’t really attempt to explain away Diaz’s stickiness, according to Carapazza.

“I told them I have a job to do,” he said. “We’re supposed to check it and that was too sticky. I can’t ignore the substance that was on there . . . I knew right when I touched it. It was way too sticky.”

Manager Carlos Mendoza said: “We gotta move on and we gotta stick to the rules . . . The rules are the rules. It’s a teaching moment. Obviously, Diaz knows, he was pretty honest with Vic and told him, hey, man, I’m a man here, I’m honest. But obviously the rules are the rules.”

The Mets will not be allowed to replace Diaz on the roster while he is suspended. That means having 25 on the 26-man roster and almost certainly playing with a shorthanded bullpen.

After an off day Thursday, the Mets will play the final eight games of Diaz’s timeout without a day off (the start of a 17-in-17 stretch).

“We’re going to have to get creative here,” Mendoza said.

Diaz technically is allowed to appeal the forthcoming suspension, but that has never yielded a reduced or eliminated punishment in these cases. Most players don’t bother.

This makes three Mets pitchers in the past season and a half to get ejected for violating the foreign substance policy, with Diaz joining Max Scherzer and Smith last year. MLB began cracking down again in 2023 to make sure pitchers weren’t gaining an unfair advantage. Sticky substances make it easier to throw pitches that move more and thus are harder to hit.

“It sucks. It sucks for everybody, it sucks for him,” Smith said. “I’ve been through it and it sucks. It makes you feel bad. It hurts the team, and personally it’s not a fun feeling.”

Mendoza said: “We gotta do a better job, bottom line.”

Diaz has been much better in three appearances since returning from the injured list, where he spent a couple of weeks with a right shoulder impingement. His numbers in those games: three innings, two hits, no runs, no walks, three strikeouts.

That represented a sudden return to form for Diaz, who pre-injury had struggled so much that the Mets removed him from the closer’s role. He had an 8.68 ERA in May, blowing four saves in five chances.

“That sucks, because I’ve been able to come back from the IL, been good and helped this team to win,” he said.

For most of the night, the highlights were six scoreless innings from Luis Severino (three hits allowed, 10 strikeouts, no walks) and home runs by Francisco Lindor, Brandon Nimmo and Mark Vientos.

Vientos’ drive went an estimated 451 feet, the longest long ball of his career and the longest by any Met this season. Lindor and Nimmo planted opposite-field homers in basically the same spot over the leftfield wall in consecutive at-bats in the third inning.

The Cubs mounted a threat only once, during Severino’s 32-pitch final frame. They put the first two batters on base to bring up their best hitters with none out. Severino retired the next three — Michael Busch via strikeout looking on a friendly call from plate umpire Alex Tosi, Cody Bellinger via strikeout swinging in a 12-pitch duel and Seiya Suzuki via flyout to center.

Called on to enter the game with no notice, Smith did his entire warmup on the field — not the bullpen — and had as long as he needed. But he “probably could’ve taken a little more time,” he said afterward.

He had trouble getting his arm loose, creating a lack of crispness in his pitches. It also was his fifth appearance in eight days.

After Smith retired his first two batters, Mendoza visited the mound with an athletic trainer. They decided Smith would face one more batter. When Dansby Swanson singled to keep the game going, Mendoza brought in Diekman.

“It’s not easy [to enter in that situation],” Smith said. “I did it to somebody last year, so maybe it’s karma. But it’s not easy. It wasn’t fun.”

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