CINCINNATI -- When Cincinnati Reds right-hander Robert Stephenson is confident throwing his fastball, it makes his secondary pitches better.

On Friday night, Stephenson had everything working, including a slider that Pirates manager Clint Hurdle dubbed "Elite." Adam Duvall and Scott Schebler homered and Stephenson had a career-high 11 strikeouts, lifting Cincinnati to a 9-5 victory over Pittsburgh in the opener of a three-game series at Great American Ball Park.

Stephenson, wearing "Bob" on the back of his jersey for MLB Player's Weekend, struck out the first six batters he faced, which according to the Reds is a modern-day franchise record for strikeouts to begin a game.

"That's pretty cool," Stephenson said. "The slider, I probably got most of the strikeouts on that. Obviously, it's easier when you're working ahead in the count. When I feel confident in my fastball, that's when I’m going to have a good game."

Stephenson gave up two runs and seven hits in 5 2/3 innings. His 11 strikeouts were the second most for a Reds pitcher this season.

"That might have been as good a slider as I've seen in a long time," Hurdle said. "The slider played exceptionally well. We hadn't seen that pitch from maybe anybody this year as far as the tilt and the depth of the slider. It was an elite slider tonight."

The Reds' offense provided plenty of cushion, led by Schebler, who went 3-for-3 with a triple, homer and three RBIs.

Cincinnati (55-74) improved to 9-2 this season against Pittsburgh.

The Pirates (61-68) began a stretch of 28 straight games against National League Central opponents. The Pirates have dropped 10 of 13.

The Pirates loaded the bases in the sixth, but Tim Adleman struck out pinch-hitter Jose Osuna to end the inning. Adleman didn't fare too well in the seventh when Josh Bell's 22nd home run, a three-run blast, cut the deficit to 7-5, but that's as close as the Pirates got.

Bell went 4-for-5 with a homer and three RBIs.

Bucs starter Ivan Nova (11-11) allowed seven runs (five earned) and eight hits, including two homers through five innings.

"I feel I made some good pitches with my changeup," Nova said. "The fastball kept missing off the plate. The only thing that was working for me was the curve."

Patrick Kivlehan's two-run, pinch-hit double increased Cincinnati's lead to four in the seventh.

Stephenson struck out the first six batters he faced and needed only 28 pitches to do it. Five struck out swinging. The streak ended when he walked Francisco Cervelli to begin the third inning.

The major league record for strikeouts to begin a game is eight, last accomplished by the Jacob deGrom of the New York Mets in 2014.

"He showed a willingness to compete over the plate," Reds manager Bryan Price said. "That comes with a lot of hard work. He made better pitches with the fastball."

Reds third baseman Eugenio Suarez extended his hitting streak to a career-high 10 games with a double in the second. He scored on Schebler's triple.

Tucker Barnhart's sacrifice fly put Cincinnati ahead 2-0.

Stephenson tied his career high with nine strikeouts in the fourth inning, but John Jaso's RBI double to center tied the score at 2.

Barnhart's RBI single put the Reds ahead 3-2 in the fourth.

Nova struck out three straight batters after the Reds loaded the bases in the fourth inning with no outs, but not before his wild pitch allowed a fourth run to score.

The Reds played long ball against Nova in the fifth when Duvall's 30th home run and Schebler's 25th gave them a 7-2 lead.

"I really had in mind (Joey) Votto, he's been really hot," Nova said. "But the other part of the lineup was the one that did damage to me."

NOTES: Pirates C Francisco Cervelli, who was reinstated from the 10-day disabled list (left wrist inflammation), left after three innings with left quad discomfort. ... Pirates C Elias Diaz was optioned to Triple-A Indianapolis. ... Reds C Stuart Turner was placed on the three-day paternity list, OF Jesse Winker was placed on the 10-day DL and OF Philip Ervin was recalled from Triple-A Louisville. ... Reds 1B Joey Votto extended his season-high on-base streak to 29 games with an eighth-inning walk.