ATLANTA — Brooks Conrad slowed up as he rounded first base, unsure if his drive had cleared the left field wall to give the Atlanta Braves an improbable victory.

Then he saw Laynce Nix swat at his empty glove in frustration.

The ball went over. Game over.

Conrad hit a pinch-hit grand slam Thursday to finish off a seven-run ninth inning that gave the Atlanta Braves a 10-9 victory over the Cincinnati Reds, who fell out of first in the NL Central and can only hope the stunning loss doesn’t leave a hangover on their surprisingly strong start.

“It was a horrible ending,” said Reds manager Dusty Baker, who appeared close to breaking down after the game. “Boy, that was a tough one.”

The Braves put together the biggest ninth-inning comeback since Cleveland rallied from six runs down against Tampa Bay on May 25, 2009, according to STATS LLC.

“I hit it and I was kind of talking to it to get out of there and I saw (Nix) jump up,” Conrad said. “From my angle ... it looked like he kind of brought it back. I put my hands no my helmet and said, ‘No way he caught that.”

He didn’t.

“I thought I had it,” Nix said. “It just bounced out.”

Atlanta fell behind 8-0 against rookie sensation Mike Leake and was still down 9-3 heading to the ninth. Four straight hits, including Nate McLouth’s two-run single, gave the Braves hope. A walk to David Ross loaded the bases with no outs, bringing the potential tying run to the plate.

Martin Prado hit a grounder to third that looked like a sure double play, but Miguel Cairo couldn’t get the ball out of his glove — Cincinnati’s fourth error of the game. Jason Heyward struck out against Arthur Rhodes on a 3-2 pitch, and Cincinnati turned to closer Francisco Cordero (1-3) for the last two outs.

Instead, Conrad hit a drive that deflected off Nix’s glove as he reached over the top of the wall at the 380-foot sign. Standing near the mound, Cordero ripped out his jersey and looked toward the dugout in disbelief.

The Braves won their third straight game in the final at-bat, beating the Reds 5-4 with Heyward’s ninth-inning double Wednesday. Atlanta has won eight of 10 to climb above .500 (21-20) for the first time since April 22.

The remarkable rally overshadowed Joey Votto’s first career grand slam, the highlight of Cincinnati’s eight-run second inning, and Leake’s attempt to improve to 5-0. Craig Kimbrel (1-0) quietly picked up his first major league win with a scoreless ninth.

Leake certainly did his part, allowing only one earned run on five hits in six innings. He gave up three runs in all, but the others could be blamed on a leaky defense that eventually caught up with the Reds. Right-fielder Jay Bruce fumbled away a fly ball at the warning track, and shortstop Orlando Cabrera dropped a throw on a potential double-play grounder.

Cabrera also mishandled a hard-hit grounder in the ninth, a play that was generously ruled a hit.

“We gave them their first three runs, and in the ninth we got two double-play balls,” Baker said. “It was shocking, all right.”

Leake, one of the few players to jump directly to the majors without any major league experience, was matched against Tommy Hanson in a showdown between two of baseball’s best young pitchers. The Atlanta right-hander didn’t hold up his end of the expected duel, giving up eight hits and eight runs in 1 2-3 innings — easily the worst start of his big league career.

Hanson escaped trouble in the first but wasn’t so fortunate in the second, even after Ramon Hernandez’s leadoff single was followed by two straight outs. Leake helped his cause with a single to center, Cabrera walked to load the bases and Cairo dumped a run-scoring single to center on an 0-2 pitch.

Leake held up at third, leaving the bases loaded for Votto. He got ahead 3-1 in the count, then made Hanson pay for a fastball just above the knees with a towering drive that easily cleared the wall in left-center.

The Reds weren’t done, either. Phillips singled, Bruce walked and Hernandez came through with his second hit of the inning to make it 6-0. Nix followed with a two-run double into the right-field corner, finally prompting Braves manager Bobby Cox to call for the bullpen.