MILWAUKEE — Robert Gsellman has been among the Mets’ most reliable bullpen options this season, and Jerry Blevins drastically less dependable. On Sunday it was exit Gsellman, enter Blevins and begin the grieving.

Blevins and Paul Sewald proceeded to dump kerosene on a campfire, with four runs scoring before the seventh inning concluded. And the Mets soon had a third straight loss, 8-7 to the Brewers at Miller Park.

The Mets (25-24) are a mess as they head to Atlanta for four games over the next three days (weather permitting), including a doubleheader Monday. The biggest recent problem has been the bullpen turning to mush, calling several of manager Mickey Callaway’s moves into question.

The latest was the decision to remove Gsellman, a key member of the bullpen, for Blevins — a lefty specialist who is struggling against lefties — to face Travis Shaw with two outs in the seventh. The lefty-swinging Shaw stroked an RBI single that pulled the Brewers within 6-5 before Paul Sewald entered and surrendered consecutive doubles that brought in three runs.

“The numbers were so drastically in favor of Blevins tonight, I thought it was a solid decision to bring him in,” Callaway said.

But the numbers Callaway cited were also small sample sizes: Shaw was 3-for-7 (.429) against Gsellman lifetime. Shaw was 0-for-2 with a walk against Blevins.

“It’s not just those two small sample sizes you pay attention to, it’s the overall numbers to suggest Blevins has a much greater chance to get the hitter out, and I think you have to go with those,” Callaway said. “I think it’s part of managing the game today. I think it’s like preparing and doing everything you can and if things don’t work out, you feel OK about it. I kinda take that same approach.”

Lefties are now 8-for-27 (.296) against Blevins. They are 8-for-45 (.178) against Gsellman. In his last three appearances to face only one batter, Blevins has not recorded an out. On Saturday, he pitched 1 ¹/₃ innings scoreless in a blowout loss.

“I don’t think I have been this angry with baseball in a while,” Blevins said. “It was a perfect kind of setup for me. I pitched all right [Saturday], I come in, Mickey puts me in a situation that is tailor-made for me. That is what I have been doing my whole career and it would have been real nice to help the team out and show Mickey the faith in me is not for naught.”

Devin Mesoraco got the Mets closer in the ninth with a solo homer before Corey Knebel got the final three outs.

Zack Wheeler had his usual one bad inning — the fourth, when he surrendered three runs (on Jesus Aguilar’s homer) — but rebounded to get through six. Overall, the right-hander allowed four earned runs on six hits and two walks, departing after 110 pitches.

“That is a good team over there,” Wheeler said. “We were feeling good coming in and we are playing good ball. Some things aren’t going our way. Maybe sometimes the pitching is there and the hitting is not and sometimes the hitting is there and the pitching is not.

“Once we all get on the same path I think we will take off and just look back and sorta laugh about this little stretch. We are a better team than what we are playing right now and I think all of us know that.”

The Mets sent 10 batters to the plate in the second inning against Jhoulys Chacin and scored four runs to take a 4-1 lead. Wheeler’s two-run single was the big hit in the inning, after Tomas Nido had singled in a run. Asdrubal Cabrera also stroked an RBI single, but the Mets had the bases loaded with one out and couldn’t extended the lead, as Wilmer Flores and Jay Bruce were retired.

Wheeler surrendered a run in the first, after Michael Conforto and Bruce converged on Aguilar’s fly to right center with indecision. The ball hit Conforto’s glove and fell for an RBI single. Flores had a throwing error in the third that allowed Lorenzo Cain to take an extra base before Aguilar homered.

“We made a couple of errors we probably shouldn’t have made that cost us some runs,” Callaway said. “It just wasn’t a clean game.”