Choo, who came into the game 5-for-his-last-33 (.182), was relieved when his line drive dropped in front of Hunter Pence, but manager Dusty Baker knew it was just a matter of time.
"He was hitting the ball hard," Baker said. "And I said, 'Hey man, you're going to get hot.' I could just see it. He may not see it, but I can see it because he was swinging the bat well, just not getting anything to show for it."
Choo's game-winning hit was his second single of the night, and it came off left-hander Javier Lopez. Entering the game, Choo was batting just .152 against lefties, who have attacked him inside all season.
"I don't want to change, try to pull the ball," Choo said. "That's not my strength. What can I do? I just keep hitting."
For Choo to even have a chance in the bottom of the 11th, the Reds needed their bullpen to come up big. And after starter Tony Cingrani allowed two runs on four hits in 5 2/3 innings, that's exactly what happened.
It started with Logan Ondrusek, who picked up one out in the sixth, before Sam LeCure struck out the side in the seventh. The top of the eighth was dicey after Alfredo Simon struck out Pablo Sandoval on a wild pitch, allowing him to race to first and extend the inning. But after a walk and a hit batter to load the bases, Manny Parra entered the game and escaped the inning with a flyout.
Aroldis Chapman came on and struck out two batters on his way through the ninth inning, setting up J.J. Hoover to pitch the final two innings and earn the win.
"Everybody that came out of the bullpen was on top of their game," catcher Devin Mesoraco said. "Those were some of the best performances that I've seen in a while from almost all those guys."
The Reds jumped out to an early lead Wednesday, thanks to a sacrifice fly from Chris Heisey in the bottom of the second. Seeing his first action at home since April 24 because of a right hamstring strain, the left fielder also connected on a solo home run four innings later after the Giants had taken a 2-1 lead on a two-run homer off Cingrani in the fifth.
Between Heisey's RBIs, the Reds struggled to capitalize on scoring chances.
In the bottom of the fourth, after a strikeout and flyout to start the inning, Mesoraco came through with his second single of the game, followed by a double from Cingrani. As Mesoraco raced toward third, he got his signals crossed with third-base coach Chris Speier, who waved him home before putting up the stop sign. It was too late, though, as Mesoraco was tagged out in a rundown to end the inning.
"I thought I would be able to score, and [Speier] was waving me," Mesoraco said. "I just thought I was kind of out there too far and in no man's land, and I wasn't sure what to do. Then I seen him throw it home, and I was thinking I was going to get back. Then I seen it got away, and I was thinking maybe I can go home. It was a little too much thinking on my part."
Once again, the Reds were presented with a prime opportunity to even the score in the next half-inning, when they had runners on the corners with no outs and the heart of the order waiting. But after a Zack Cozart single, Giants manager Bruce Bochy brought in lefty Jose Mijares, who struck out Joey Votto. He then called upon right-hander George Kontos, who fanned both Brandon Phillips and Jay Bruce.
Bochy said he wasn't going to hold anything back when it came to pitching substitutions, as his team is now 1-9 in its last 10.
"We're doing all we can to win a game right now," Bochy said. "That's why this was a tough one."
Meanwhile, Baker had the luxury of a fresh bullpen after Homer Bailey's no-hitter Tuesday and Bronson Arroyo's six-inning complete game Monday that was called due to weather.
"We were down to our last man [Curtis Partch], and they were down to their last man [Sergio Romo]," Baker said. "We cleared the benches trying to win that game. It was a good game."
Frazier led off the game-deciding 11th with a walk and advanced to second on a Heisey sacrifice bunt. With one out and first base open, Lopez intentionally walked Mesoraco, who had a career-high three hits on the night.
Although pinch-hitter Ryan Hanigan couldn't make the Giants pay, Choo did in the next at-bat, giving the sellout crowd a reason to celebrate for the second straight night.
Cincinnati, following a 2-6 road trip, has now won three games in a row for the first time since June 10-12 against the Cubs. With a Pirates win, the Reds remained four games back in the National League Central, but they have built back some of the momentum they lost in the last couple of weeks.
"The road trip was pretty bad, but that's baseball," Frazier said. "It's the most humbling sport in the world. You got to understand that you go to play this game inning by inning, game by game and not worry about 2-6 and worry about the next day. We grind a win out today, we're pretty tired, but we'll be ready to go tomorrow."
Jeremy Warnemuende is an associate reporter for MLB.com.