CINCINNATI — One step forward and another backward for Kodai Senga.

After receiving his best results of the season in his previous start — six shutout innings against the Rockies last week — the Mets right-hander was on the verge of removal before recording three outs against the Reds on Thursday.

Senga survived the first inning, but the Mets never recovered in their 5-0 loss at Great American Ball Park.

Tommy Hunter was warming up in the bullpen as Senga faced his ninth batter of the first inning.

Curt Casali struck out, ending the inning at 37 pitches for Senga, who had fallen into a 4-0 hole.

“One thing I had in mind coming into this outing was pounding the strike zone, which I thought I did pretty well,” Senga said through his interpreter. “But I happened to throw it where they could hit it.”

Senga had two outs with a runner on second in the first when Jake Fraley got jammed and singled in a run.

The ensuing batter, Tyler Stephenson, hit a check-swing single through the first-base hole.

Nick Senzel’s RBI double and Kevin Newman’s two-run single brought in the additional runs in the inning.

“I think those weak hits turning into hits … there’s not much you can do about it,” Senga said. “But to let in those runs in the first inning it’s hard to get the team in a groove, so it’s something I need to work on.”

Senga didn’t allow another run until the fifth, when Spencer Steer homered against him.

The five runs allowed were a season-high for Senga, who walked only one batter over his five innings. Senga walked four batters in each of his previous four starts.

Senga’s four-seam fastball averaged 94.7 mph, down from his season average of 96.

The average velocity on his cutter was 88.9 mph, down from his season average of 90.3.

“I think when you throw that many pitches in one inning it takes a toll on your body,” Senga said, referring to the first inning. “It drains the stamina out of you a little bit, so in order to not do that I need to be a little more economical and to limit the damage. I know where they are going to do damage, so pitch away from that.”