CINCINNATI -- With the Mets’ postseason hopes hanging by a thread, they need gutsy efforts like the one Marcus Stroman delivered on Sunday afternoon against the Reds at Great American Ball Park.

Stroman has been dealing with nausea over the past couple of days. He began feeling sick again in the bullpen prior to Sunday’s outing. But after overcoming a rough first inning, the right-hander retired 13 in a row to set the stage for a critical 6-3 victory. The Mets now sit 4 1/2 games behind both the Brewers and Nationals in the National League Wild Card race, with seven games left to play.

Stroman allowed two runs over 4 2/3 innings. The Mets got almost all their offense from the long ball, with home runs by Michael Conforto, J.D. Davis and Brandon Nimmo. New York took two of the three games in the weekend series.

• Box score

“It was just hard to get my stomach in order,” said Stroman, who made his first career start in Cincinnati. “The past couple of days, I haven’t felt too good.”

The Mets jumped on Reds starter Trevor Bauer in the first inning with back-to-back two-out doubles by Pete Alonso and Robinson Canó that gave them an early 1-0 lead.

“It means a lot to finish strong,” said Alonso, who heads to Citi Field two home runs shy of Aaron Judge’s rookie record of 52. “I don’t want to go into the offseason with a sour taste in my mouth.”

Canó was hit in the left foot by a pitch in the third inning, and he left the game in the fourth. X-rays on his left big toe were negative.

“It’s a little sore,” said Mets manager Mickey Callaway. “There’s a lefty going tomorrow, so maybe a day off [for Canó]. But it’s nothing we’re too concerned about.”

After Wilson Ramos was hit by a pitch following the doubles in the first, Conforto jumped on a 2-0 pitch from Bauer and sent it 415 feet, according to Statcast, into the right-field seats for a three-run home run, his 31st, making the score 4-0.

“We love to see that sweet swing,” said Callaway. “It’s a good sign. His [home runs] come in bunches.”

Following Conforto’s homer, Bauer retired 14 of 15 Mets batters without allowing a hit, until Davis’ 20th homer in the sixth. Nimmo added another run with his eighth homer of the season in the ninth.

After allowing a run and two hits in the first, Stroman set down 13 straight before allowing Kyle Farmer’s solo home run with two outs in the fifth.

Things unraveled for Stroman after Farmer’s homer. He issued three straight walks to load the bases, including one to Bauer, who had previously walked only once this season.

Stroman, who had walked two or fewer batters in six of his previous nine starts with the Mets, wasn’t about to use his illness as an excuse.

“No one is tougher on myself than me,” he said. “That’s not like me to walk three straight guys. My stuff felt great. I just beat myself with the walks.”

Brad Brach bailed out Stroman by getting Eugenio Suárez to pop out to end the inning.

“Very impressive effort,” Callaway said of Stroman. “He was nauseous and felt the effects of it, pretty violently. We knew after he warmed up. He probably could have gone six [innings] if he hadn’t walked the pitcher.”

And with Stroman’s effort, the Mets’ Wild Card hopes are still alive.

They now return to Citi Field for their final seven games of the season, with four against the Marlins and three against the Braves.

“We’re playing good baseball,” Callaway said. “We just need to continue to put pressure on others and keep moving forward and focus on one game. We’re [still] playing for something.”