Atlanta took a 5-0 lead against starting pitcher Homer Bailey, including a 3-0 lead after four batters on Justin Upton's three-run homer.
Catcher Devin Mesoraco could be headed for the disabled list after he strained his left hamstring while scoring a run in the seventh.
"The severity is it could be significant or it could be something that's a couple or three days," Reds manager Bryan Price said. "We'll see. I think we'll have more news for you tomorrow."
Third baseman Todd Frazier has a tight left groin, which surfaced during a leadoff double in the second inning. Frazier exited before the bottom of the fifth.
"To come out is really tough," Frazier said. "I don't like coming out of games. Every game is important to me. If they really needed me out there … if it was a playoff game or something, I'm not coming out."
Bailey allowed five runs and nine hits over six innings with no walks and four strikeouts. Through five starts, he has allowed at least four runs in four of them and he leads the National League in homers allowed with seven. Upton's drive to left field came on a 2-2 offspeed pitch following singles by B.J. Upton and Freddie Freeman.
In the second inning, Jason Heyward lined a two-out single to center field to score Andrelton Simmons. The fifth Atlanta run scored in the third inning when Evan Gattis blooped a one-out single to left field that scored Freeman.
With a 1-2 record and 6.15 ERA, what's been the issue for Bailey?
"Bad pitches, typically does it," he replied. "It's kind of one of those that I just have to sharpen up just a little bit. One pitch here, one pitch there. I'd probably be a little more worried if I were walking a bunch of guys or getting behind in a lot of counts. It's simple pitch execution. It's what I'm not doing in big situations."
The Reds were able to inch their way back into the game against Braves starter Ervin Santana, who came in with only two runs allowed over his first three starts.
In the first inning against Santana, Cincinnati had runners on first and third base with one out. Jay Bruce flied out to right field, and although the ball was not hit deeply, third-base coach Steve Smith tested Heyward's strong arm and had Joey Votto tag up and try to score. Votto was easily thrown out sliding head first into the plate for a double play.
Santana cruised after that, including a five-pitch fourth inning and nine-pitch fifth, before the Reds put something together in the sixth. Votto led off with a walk and Brandon Phillips laced a double to left field. Bruce's RBI single scored Votto with the first run, and another run crossed when Neftali Soto grounded into a double play.
In the seventh, Mesoraco led off with a single and advanced on a Santana wild pitch to Zack Cozart. With two outs, as Billy Hamilton rolled a hit up the middle and hustled for a double, Mesoraco grabbed his left hamstring and fell down after rounding third base but limped home to score.
"It balled up once I got my right foot off the bag and once my left foot planted there, it kind of balled up," Mesoraco said.
Votto made it a one-run game with his lined single to center field against lefty reliever Luis Avilan.
"We fought though. I was watching it here when I was getting treatment," Frazier said. "That's a big step. We fought -- I'm proud of our guys for that -- to the very last out. We didn't give up a run after the five we gave up. I'm just happy we fought and kept swinging."
In the ninth against closer Craig Kimbrel, the comeback was almost completed. Roger Bernadina hit a leadoff single, and Cozart's four-pitch walk put the go-ahead run on first base.
"In the pit of your stomach, you're thinking this is a good-hitting club, and we've got some opportunities and we haven't added on after the third," Braves manager Fredi Gonzalez said. "Sure enough, they got first and second with nobody out there in the ninth inning."
With two outs, Votto hit a ground ball to third base where Chris Johnson made a wide throw to Freeman at first base that appeared initially to have pulled him off the bag. Votto was called out by umpire Vic Carapazza, but Price came out and requested a manager replay challenge.
The out call was confirmed after a two-minute, seven-second review, and the game was over in bizarre fashion.
Had Votto been ruled safe, the Reds could have tied the game since Bernadina never stopped running after reaching third base. Price sought out the crew chief after the decision.
"I wanted to know if it was inconclusive or if it was confirmed," Price said. "And it was confirmed. I had a chance to come up here and look at our own video, which is what they're getting in New York. And it was a confirmed out call. They got the call right in the end."
Price was disappointed with the outcome, but not the effort.
"If you have to lose, at the end of the day, you hope you have some things to look back on," he said. "We came back and pushed and pushed and pushed. The guys were into it and had great energy on the field and played hard. Homer bounced back after a tough three innings and gave us a chance to get back in the game. The bullpen came in and did a real nice job. We defended well and we did a lot of things well. We just came up short."