CINCINNATI -- Scott Schebler played for more than a month with a left shoulder strain, not realizing to what extent it was affecting his hitting.

"I didn't realize how important it is," Schebler said. "I thought it was my non-dominant shoulder. I just needed to rest it."

On Tuesday night, Schebler hit a grand slam and tied a career high with five RBIs, and Adam Duvall added a three-run shot in the ninth inning, lifting the Cincinnati Reds to a 14-4 victory over the New York Mets in the opener of a three-game series at Great American Ball Park.

Since coming off the disabled list on Aug. 18, Schebler is hitting .387 with three doubles, a triple, three home runs and 11 RBIs.

"This kid has an opportunity to be a real beast of a ballplayer," Reds manager Bryan Price said. "The ability to hit. The on-base percentage is in there. We've seen that since he's come back."

Cincinnati (56-76) snapped a 14-game losing streak to New York dating to 2014 and an eight-game head-to-head skid at Great American Ball Park.

Eugenio Suarez went 3-for-4 with a double and a RBI, and rookie right-hander Sal Romano (4-5) allowed three runs and six hits through six innings.

Joey Votto drew three walks and hit an RBI single in the ninth. His walk in the first inning was his sixth in six consecutive plate appearances.

It was a rough evening for the Mets (57-74), who lost for the 12th time in 16 games after learning Monday that they likely would be without third baseman David Wright and outfielder Yoenis Cespedes for the rest of the season.

Chris Flexen (3-3) made his first career start for the Mets against the Reds and allowed seven runs and seven hits in 4 2/3 innings. He allowed Schebler's grand slam in the first and left trailing 6-1.

"Not sure," said Mets manager Terry Collins, when asked about Flexen's first-inning struggles. "The only thing I think he's probably excited about starting the game, and once he gets into the flow of the game, he settles down. He limited the damage and then they caught up to him in the fifth, I think he was running out of gas a little bit."

Mets first baseman Dominic Smith snapped an 0-for-12 skid with a two-run single in the sixth. He went 2-for-4.

Things unraveled for the Mets in the eighth when Cincinnati sent 12 batters to the plate and scored seven times.

Duvall's three-run homer, his 31st home run of the season, came off Chasen Bradford, who didn't retire batter and allowed seven runs (four earned).

Mets catcher Kevin Plawecki made his second relief appearance in the eighth.

He got pinch-hitter Phillip Ervin to ground into a double play, but a run scored. He also allowed an RBI double by Billy Hamilton, who earlier in the inning singled and scored.

Jose Reyes walked and scored on Asdrubal Cabrera's double to put the Mets ahead 1-0 in the first, but the lead was brief.

In the bottom half, Suarez's RBI single and Schebler's grand slam to right field put Cincinnati ahead 5-1.

It was Schebler's 26th home run of the season and first career grand slam. The Reds have six grand slams this season. The club record is nine.

"I didn't see his fastball very well," Schebler said. "It was a changeup that I hit out."

Cincinnati added to its lead in the fifth when Scooter Gennett's infield single off Flexen's leg drove home Zack Cozart from third, making the score 6-1.

Schebler singled in a run off Josh Smoker in the fifth to increase the Reds' lead to 7-1.

Romano settled down after the rough first inning, retiring seven straight batters in one stretch.

"I felt really sharp today," said Romano. "I pitched to a lot of contact today. It's 14 in a row they beat us. Nice to get a win today."

NOTES: Mets 3B David Wright terminated his rehabilitation assignment and will be examined in New York later this week after his shoulder pain didn't subside. ... New York RHP Matt Harvey (shoulder) will return from the disabled list to start Friday vs. Houston. ... Mets RHP Noah Syndergaard (torn right lat) will throw a 25-pitch bullpen session on Wednesday. ... Jose Reyes made his first career appearance in left field for the Mets. It was just his second career start in the outfield. ... Reds 1B Joey Votto made his 1,400th appearance, moving him past Edd Roush into 10th place on the club's games played list.