Todd Frazier's solo home run to right field with one out in the bottom of the ninth inning sent Cincinnati to a 2-1 win over Atlanta in the third contest of a four-game series.
Facing Cristhian Martinez (2-1), Frazier drove an 0-1 pitch barely over the wall for his fourth homer of the year, giving the Reds their fifth walk-off win of the season.
"I was just focused on getting on base," Frazier said. "I couldn't have asked for anything better."
Jay Bruce drove in the other run for Cincinnati, which won its season-high fifth straight contest.
Bronson Arroyo, who was making the 300th start of his major league career, allowed four hits, walked two and had seven strikeouts over 6 2/3 innings in the start for the Reds. Ardolis Chapman (4-0) fanned a pair of batters in the ninth to get the win and has yet to allow an earned run in 24 1/3 innings this year.
Tommy Hanson threw six frames, yielding four hits and a run while fanning five for Atlanta.
Dan Uggla homered in the fourth inning, a leadoff shot that reached the second deck in left field and provided the Braves with their only run.
"It's tough to win games when your offense is not clicking," Braves manager Fredi Gonzalez said.
The Reds loaded the bases in the sixth thanks to singles from Zack Cozart and Chris Heisey, and a one-out walk to Brandon Phillips. Bruce then beat out a potential double-play grounder, allowing Cozart to come home.
Phillips, a three-time Gold Glove winner, made a spectacular defensive play in the seventh inning that probably saved a run. Tyler Pastornicky doubled with two outs and then pinch-hitter Chipper Jones drew a walk from reliever Jose Arredondo. Michael Bourn sent a ground ball toward the middle, but Phillips made a tumbling stop, and from his back flipped the ball to Cozart at second to get pinch-runner Tim Hudson just in time.
The Reds threatened in the eighth with one out and men at the corners, but Bruce grounded into a 4-6-4 double play, immediately after Eric O'Flaherty relieved Jonny Venters.
Jones was out of the starting lineup because of a bruised left calf...The teams combined to go 0-for-11 with men in scoring position...Martin Prado had two of Atlanta's four hits, while Cozart and Heisey each had a pair of hits for Cincinnati.