David Peterson bent over behind the mound in Sunday’s fifth inning, giving the appearance of perhaps a back ailment.

To the Mets’ relief, the left-hander merely was dealing with nausea.

“I threw a pitch, and I got the ball back, and then my vision just went blurry,” Peterson said after the Mets beat the Blue Jays 2-1 at Citi Field. “My vision started to come back, and then my stomach turned over on me. I just felt worse with every breath I took, and it just felt like I got punched in the stomach and was going to throw up.”

But Peterson managed to talk his way into remaining in the game to face two additional batters, neither of which were retired.

The Mets averted disaster as Max Kranick escaped a bases-loaded jam to preserve the lead.

“The last thing you want to see is a guy bend over like that, it’s not a good look,” manager Carlos Mendoza said. “Once I got out there and I heard ‘stomach’ and ‘not feeling good,’ I was like, ‘OK, this is not an arm or anything we have to worry about. Just take your time and see how you go.’ ”

Mendoza said he stuck with Peterson for the additional batters in an attempt to get through the inning without utilizing the bullpen.

Peterson extended to 91 pitches as he walked Anthony Santander and plunked Andrés Giménez, forcing in a run.

Peterson said he was examined by team medical personnel but didn’t have any additional symptoms.

Brett Baty went 0-for-3 with two strikeouts and saw his slash line drop to .095/.095/.143.

Baty, who has 21 plate appearances, is serving as the primary second baseman with Jeff McNeil (oblique) on the injured list.

“They keep throwing fastballs by him,” Mendoza said. “I think he’s a little off timing-wise because he’s either clinging to the fastball or chasing offspeed pitches out of the strike zone. He will continue to fight, continue to work and he will get through it.”

Luis Torrens was absent for a second straight start behind the plate because of a forearm contusion.

Torrens was a late scratch from Saturday’s lineup but entered as a defensive replacement.

“He’s still sore,” Mendoza said, adding that Torrens was available if needed.

Hayden Senger started a second straight game and reached base twice.

The Mets drew 121,771 fans to Citi Field for their opening series.

Last season, the team drew only 94,655 for the first three home games.