Cairo led off the 10th against lefty Phil Coke by hitting a line drive to the right-field corner. As Matt Young struggled to retrieve the ball, the 38-year-old Cairo -- who was out with a hamstring injury early in the season -- lumbered into third base with a stand-up triple.
With the Detroit infield playing in, Ryan Hanigan hit a ground ball to third base that forced Cairo to hold. Next up was Valdez.
"He [Valdez] was looking at me and I was like, 'Here we go,'" Cairo said. "I said, 'Please don't pull a hamstring right here.' I was expecting it, and I know he likes to do it."
Valdez bunted a first-pitch sinker from Coke to the right side. Upon contact, Cairo broke for home and slid head-first safely, just ahead of Prince Fielder's throw to the plate.
"We were certainly aware of it, obviously," Tigers manager Jim Leyland said. "It was just a good call and the guy executed it. I thought Prince made a good play on the ball."
Ruled a sacrifice bunt, it was the first time the Reds won a game on a walk-off sacrifice bunt since Jeff Reed dropped one down against the Giants in the 12th inning on June 26, 1990 -- the year the Reds last won a World Series.
"It was great execution," Reds manager Dusty Baker said of Valdez and Cairo. "Sometimes, an average isn't indicative of what a guy means to your ballclub and what he can do. Everybody wants to contribute. Everybody wants to do something to help us win. Hopefully, we might look back on this game as one of the key games this season."
Cincinnati had a 4-0 lead through three innings and couldn't make it hold up before winding up in a topsy-turvy game.
"They're such a good offensive team that four runs generally isn't enough," said Reds first baseman Joey Votto, who was largely responsible for the early lead.
In the bottom of the third, Zack Cozart and Chris Heisey began an eight-batter rally with back-to-back singles. On a 2-1 offspeed pitch from Tigers starter Rick Porcello, Votto tattooed a drive off of the batter's eye in center field for a three-run home run and four-run lead.
Votto, who also had an infield hit in the first and a double in the fifth to be a triple shy of the cycle, extended his hitting streak to a career-high-tying 14 games.
One of the game's best hitters is also one of the hottest. Votto is batting an astounding .549 (28-for-51) with three homers and 13 RBIs during his hitting streak.
With the exception of a Brennan Boesch leadoff homer in the fourth, Reds starter Mat Latos enjoyed a largely smooth night through his first five innings. A leadoff ground-rule double in the sixth by Young led to a bases-loaded, no outs situation for Latos. Miguel Cabera drove in two runs with a rolling single into left field to make it a 4-3 game.
In the Detroit seventh, Latos gave up a leadoff single to Ramon Santiago. As Young struck out, Santiago stole second base and took third on catcher Hanigan's throwing error. Jose Arredondo took over and after notching the second out, gave up Boesch's game-tying single up the middle.
In the eighth, Arredondo gave up a 441-foot solo home run to left-center field by Delmon Young. The Reds got the run back in the bottom of the eighth after Cairo hit a leadoff single against lefty reliever Duane Below. Hanigan's sacrifice moved Cairo to second base. Right-hander Jose Ortega, making his big league debut, took over to face Todd Frazier as a pinch-hitter. Frazier, who was scratched from the lineup due to back spasms and replaced by Cairo, delivered with a game-tying RBI double to left field.
Frazier is 6-for-7 this season as a pinch-hitter.
"It was stiff, but loosened up later," Baker said of Frazier's back. "Thank God for us. It was a key pinch-hit."
Reds reliever Sam LeCure retired all six batters he faced, with three strikeouts, in the ninth and 10th innings to get the victory. The Reds were without closer Aroldis Chapman and set-up man Sean Marshall, who were not available.
"It was a big spot in the game there," LeCure said. "We were up, they battled back and it was kind of back and forth with the momentum all night."
And it ended in the Reds' favor, not because of a big, booming hit, but instead by a perfectly crafted bunt by Valdez.
"He works on it," Baker said. "He's good at it and confident about it. That was an outstanding judgment by Miggy on when to run and a great slide at home plate. That's big when you win games like that, especially after we lost a game like that yesterday."