Schebler added a tiebreaking two-run drive in the sixth, helping last-place Cincinnati salvage the finale of the three-game set.
“Your corner outfielders have got to be productive offensive players,” Riggleman said, “and both of them are heating up a little bit.”
Both of Cincinnati’s homers came off Patrick Corbin (5-2), who gave up a season-high six runs and eight hits in six innings. The left-hander struck out 10, walked one and threw two wild pitches.
“I thought I was making some good pitches there,” Corbin said. “It was just those two I’d obviously like to have back.”
Paul Goldschmidt and John Ryan Murphy went deep for the Diamondbacks, who have dropped 16 of 20 overall.
Cincinnati right-hander Sal Romano (3-6) pitched five innings in his first win since May 4, yielding four runs and seven hits. He was 0-3 with a 12.79 ERA in his previous three starts.
Raisel Iglesias got four outs for his ninth save in his first appearance since being sidelined by a biceps injury. Pinch hitter Daniel Descalso and Jarrod Dyson singled to start the ninth but Goldschmidt fouled out, Duvall made a sliding grab of Jake Lamb’s sinking liner to left and Murphy popped out.
Corbin was cruising with a 4-0 lead when Tucker Barnhart and Votto opened the fourth with singles and Suarez walked on a 3-2 pitch to load the bases. That brought up Duvall, who hit a drive into the seats in left-center for his second career grand slam.
“That at-bat went from real bad to real good real quick,” Duvall said. “I took a first-pitch strike right down the middle, a first-pitch fastball that I thought was a slider. The pitch after that I swung at one kind of in the dirt. But it was good to see one up and put the barrel to it.”
Suarez opened the sixth with a single, Duvall struck out and Schebler launched a shot 433 feet to right.
“I got that one pretty good,” Schebler said. “He threw me about eight straight sliders, just finally got one up. … After throwing it that many times it seemed like he was going to keep coming with it until I proved I could hit it.”
It was a disappointing finish for Arizona after a fast start.
Dyson led off the first with a single and Goldschmidt, moved up to second in the batting order in recent games, knocked Romano’s 1-1 pitch into the visitor’s bullpen for his seventh homer of the season. After Jake Lamb flew out, Murphy doubled to the left-center gap and scored on David Peralta’s single, sliding in just ahead of Billy Hamilton’s throw from short center field.
Murphy’s fourth home run in his last six games made it 4-0 after three.
Reds: Following an off day, Tyler Mahle (3-6, 4.76 ERA) starts Friday night at San Diego. The Reds finish a nine-game trip with three against the Padres.