Rain delayed the start of the game by 1 hour, 20 minutes, the 10th delay at SunTrust Park this season and the third in the last four games.
The NL East-leading Braves have won eight of 12. They improved to 2-7 in extra innings.
Luke Jackson (1-0), the seventh Atlanta pitcher, faced four batters in the 11th to earn the win. Floro (0-1) was the Reds' sixth pitcher.
Braves reliever Lucas Sims blew a two-run lead in the sixth, allowing three straight singles, issuing a bases-loaded walk and giving up an RBI groundout to pinch-hitter Adam Duvall that made it 3-all.
Scott Schebler doubled to begin the seventh, advanced to third on a sacrifice bunt and made it 4-3 on Joey Votto’s RBI groundout. The Braves tied it at 4-all in the seventh on Santana’s RBI double.
Atlanta starter Mike Foltynewicz, reinstated from the disabled list with right triceps tightness, allowed one run, one hit and four walks in five innings. He struck out four while throwing 91 pitches.
Foltynewicz gave up his first hit to Schebler, whose 10th homer cut the lead to 2-1 in the fifth. Over his last eight starts, Foltynewicz has a 0.96 ERA.
“He had a really fresh arm and just pounded the zone on us and made us work,” Schebler said. “We made him work as well. We weren’t going down easy. We were grinding out at-bats and made him get out of the game probably a lot quicker than he wanted to.”
Reds starter Tyler Mahle loaded the bases with no out in the fifth before a groundout put the Braves up 3-1. Mahle gave up hits, three runs and four walks with five strikeouts in five innings.
Cincinnati was coming off a four-game home sweep of the Chicago Cubs and had won 10 of 12, but the Reds are still stuck in last place in the NL Central, five games out of fourth place.
"Schebler gave us a chance a couple of times," interim Reds manager Jim Riggleman said. "Tough one to lose, but we did a lot of good things again, and if we play like that we're going to win a lot of ballgames."
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