Terry Collins believes there are meaningful games for the Mets in September, and the manager proved it by getting tossed out of Sunday’s game.

He was pleased that Jacob deGrom returned to form, but that was about it as the Mets’ bullpen failed in a 10-5 loss to the Reds at Citi Field.

DeGrom survived a two-run first inning and struck out 10 in six innings. “I would say I used my changeup more today, had a good feel for it, which I think made the slider that much better,’’ he said.

DeGrom was lined up for his 15th victory after the Mets scored three in the sixth on Dominic Smith’s home run and a two-run double by Jose Reyes for a 5-2 lead. But Paul Sewald gave up a tying three-run homer to Zack Cozart in the seventh.

In the eighth, Jeurys Familia came in for the second straight game. He gave up what turned out to be a two-run double to left-center by Tucker Barnhart.

A replay overturned the initial call by plate umpire Shane Livensparger, who ruled that Scott Schebler was out at the plate on Amed Rosario’s relay.

The Reds challenged the out call and prevailed. Collins ran out to ask umpire Jerry Layne for an explanation, which, as Collins was aware of by rule, triggered an immediate ejection.

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“I want to know what they were told,’’ he said. “I looked at the replay five times. And there was not one thing that I saw that could have possibly overturned it. For me. I just wanna know what [Layne] was told. I want to know what they saw that we didn’t see. He said he couldn’t tell me. He said, ‘He’s safe.’ ”

Travis d’Arnaud agreed with the final ruling after watching a replay between innings. “The glove stayed on my knee as I was rotating to absorb the slide,’’ he said, “and so I just missed him.’’

Collins had his choice of relievers to pick on — Barnhart hit a three-run homer off Hansel Robles in the ninth — but said of Familia: “I come in here every day and you guys want to know when he’s going to close. If you’re gonna close, you got to go back-to-back . . . We’re in a stage of trying to find out some things. We found out he’s not ready to go back-to-back.’’

Familia, who pitched in consecutive games for the first time since returning from blood clot surgery, said: “I don’t feel tired, but at the same time, I think I’m trying too much. I’m just trying to get to the point where I’ve always been when I’m healthy 100 percent. But like I said, I lost three months of the season. I gotta keep working on my delivery and see what happens.’’

Notes & quotes: Rosario had a single in three at-bats after missing six games with swelling in his right index finger . . . Pinch hitter Asdrubal Cabrera was diagnosed with a contusion of the right ankle after he was hit by a pitch in the sixth inning . . . Syosset-born Sal Romano started for the Reds, giving up two runs in five innings.