CINCINNATI -- Rich Aurilia hadn't played first base enough to figure out if he'd messed up.
Ronny Paulino hit a tiebreaking RBI single in the eighth inning, Jason Bay homered and drove in three runs and Ryan Doumit also homered for the Pirates, who kept the Reds 3½ games behind San Diego in the National League wild-card race.
Jose Castillo was on third base with one out and the score tied at three in the seventh inning when Chris Duffy hit a sharp one-hopper that Aurilia grabbed a step away from the bag. He took a quick glance at Castillo, who broke for home when Aurilia turned his head to step on the bag.
Castillo beat Aurilia's throw with a slide across the plate. Though the Reds tied the score with a run in the top of the seventh, Pittsburgh regained the lead on Paulino's single in the bottom of the inning.
Aurilia was surprised to see Castillo break for the plate, he said.
"When I looked at him, he wasn't," said Aurilia, who played one game at first base in his career before making 32 starts there this season. "In all honesty, that's a play I've never encountered in my career, because I haven't played much first base. In hindsight, I guess I should have just tagged the runner. I don't know if I can say I messed up or not. I didn't turn my body, I just turned my head to find the bag. If I messed up, it's my fault. If not, it's a great read by him."
The Reds went into the game tied with Florida for fourth place in the NL wild-card standings, one-half game ahead of Houston. They also went into the game in second place in the Central Division, one-half game ahead of the Astros.
"This is another tough one, tough in the sense that we could have climbed back to within 2½ in the wild card," said Aurilia, who had three hits for the fourth time in his last five games.
The Reds tied the score again in the bottom of the seventh on Royce Clayton's sacrifice fly. Freddy Sanchez singled off Todd Coffey (6-6) to lead off the eighth, snapping an 0-for-11 slump. He moved to second when Bay walked and reached third two outs later on Coffey's wild pitch.
Paulino followed with a line-drive single to center field to make a winner of Matt Capps (7-1), who gave up Clayton's sacrifice fly in the seventh. Bay added a two-run double in the ninth, giving him 101 RBIs and making him the first Pirates player to hit at least 30 home runs and drive in at least 100 runs in consecutive seasons since Brian Giles in 1999 and 2000.
"You can't argue with what the guy's done," manager Jim Tracy said. "He'll continue to get better. I firmly believe that."
"I'm pleased with the numbers, but I've still got a lot of work to do," said Bay, an All-Star starter this season.
Sanchez went 1-for-5 to drop his NL-leading average one point to .340.
John Grabow got two outs in the eighth inning and Salomon Torres got the last four for his fifth straight save after blowing his first two chances this season.
Pittsburgh starter Paul Maholm went six innings, allowing six hits and three runs with two walks and six strikeouts.
Reds right-hander Aaron Harang, winless in four starts since beating Pittsburgh 5-1 on Aug. 20, gave up eight hits and four runs with no walks and five strikeouts in seven innings.
For the second consecutive night, the Reds scored in the first inning. Clayton singled and Aurilia doubled with one out, setting up Edwin Encarnacion's sacrifice fly.
Bay led off the second inning with his 32nd homer, matching his career high set last season and tying the score.
Pittsburgh took a 2-1 lead in the third on Chris Duffy's leadoff triple and Sanchez's one-out RBI grounder. Doumit made it a 3-1 lead with his fourth homer in the fourth.
The Reds tied it in the bottom of the fourth. After Adam Dunn walked with one out, Brandon Phillips hit his 16th home run of the season -- and first in 34 at bats since Aug. 29.
The switch-hitting Doumit has hit all four of his home runs left-handed. ... Harang extended his streak of consecutive starts without allowing more than three walks to 76 -- the fourth-longest current stretch in the majors. ... Phillips had two hits in his last 31 at bats before his home run. ... Coffey celebrated his 26th birthday Saturday.