The D-backs, despite losing 10 of 15 overall, have taken two of the first three against the Reds, including Wednesday's 7-1 win. That contest dropped Cincinnati back into a tie with Pittsburgh atop the National League Central.
Joe Saunders will try to help Arizona capture the series in his second start since coming off the disabled list. The veteran lefty is 4-6 with a 3.52 ERA this season.
He managed a quality start on Saturday at Wrigley Field, taking the loss, but holding the Cubs to three earned runs on eight hits in six innings. Saunders struck out four and walked none.
"I felt great," Saunders said afterward. "It was fun to get back out and start contributing again."
The Reds will counter with Mike Leake, who has been strong of late after a rough start to the season. The righty was 0-5 with a 7.11 ERA on May 11, but owns a 2.59 mark over his last 11 outings, including 1.95 over his past five.
Leake didn't get a decision on Saturday against the Cardinals, but gave up only two runs in six innings.
D-backs: Bullpen getting the job done
Arizona manager Kirk Gibson didn't have to ask his bullpen for much on Wednesday, as starter Ian Kennedy threw eight strong innings and left with a big lead.
But when called upon, D-backs relievers have been answering. The club entered the day leading the NL with a 1.91 bullpen ERA since June 22, and the 'pen has logged 9 1/3 scoreless innings in this series.
"Our bullpen has done a good job," Gibson said. "It's been really the story of who scores first."
Left fielder Jason Kubel didn't show any rust on Wednesday, when he returned to the lineup after missing four games with tightness in his hamstring. Kubel homered in his first two chances and also drew a walk in five plate appearances.
Reds: Paul gets a chance to contribute
Xavier Paul flew out as a pinch-hitter in his first appearance with the Reds on Wednesday, but the 27-year-old outfielder figures to receive more opportunities to serve as a left-handed bat off the bench.
The Reds signed Paul after he opted out of his contract with the Nationals' Triple-A affiliate in early July, and then called him up to Cincinnati on Wednesday. Paul was hitting .332 in 66 games at Triple-A this season, and the Reds needed someone to balance their righty-heavy roster, with Joey Votto on the DL.
"I liked him when he was with the Pirates," manager Dusty Baker said. "He was one of the best pinch-hitters around, especially against right-handers. He can play all three outfield positions and gives us that much needed left-handed bat. He has speed, which we also need."
Paul played for the Dodgers and Pirates from 2009-11, hitting .246 with a .629 OPS in 411 plate appearances.
Right fielder Jay Bruce is hitting .119 (5-for-42) with one home run in his last 11 games. His OPS, at .807, is at its lowest point since April 26.
After this game, the two teams will meet again Aug. 27-29 in Phoenix.
Saunders' only career start at Great American Ball Park came in 2010, when he gave up seven runs, four earned, in 7 1/3 innings.
Leake has allowed nine earned runs over 11 2/3 innings in his two career starts against the D-backs, which both came last season.