The Reds have won a season-high five consecutive games. It's their longest winning streak since a season-high six-game streak last August.
With the Reds trailing, 2-1, in the ninth, Joey Votto singled and Edwin Encarnacion was hit by a pitch. Reds manager Dusty Baker called upon Dunn, one of the club's most adept bunters, to advance the runners to second and third.
"He's one of the best bunters we have," Baker said. "We couldn't afford a double play in that situation. That's baseball. He's been bragging to me since Spring Training that he can bunt. He got a pitch to hit, and he lost it."
Facing Tribe reliever Masahide Kobayashi, Dunn made two bunt attempts, fouling off the second pitch. With the count 1-1, he chose to swing and took a ball.
Dunn launched Kobayashi's 2-1 delivery into the afternoon sky for his ninth home run of the season, and seventh career game-winner.
"For me, it's the best feeling you can have on a baseball field," Dunn said. "We had opportunities to score early in the game and we didn't. It's hard to win in the ninth inning. Year after year, we seem to get it done in the ninth. I don't know why that is, but I love it."
Indians manager Eric Wedge was amazed to see the Reds' burly slugger square to bunt on Kobayashi's first delivery.
"Yeah, I was a little bit surprised," Wedge said. "But he's a good athlete. That's obviously a direction they can go. In the end, obviously, he wasn't going to do that."
Dunn's heroics erased what could've been an especially frustrating loss for the Reds.
Starting pitcher Aaron Harang, who's endured a lack of run support throughout the season, allowed just one run on eight hits in seven innings. The Reds have averaged just 3.4 runs in his 10 starts.
"He's going to get wins. When he gets them, they'll come in bunches. Right now, we're getting wins. That's what is important."
-- Dusty Baker, on pitcher Aaron Harang
Harang engaged in a classic pitchers' duel Saturday with Indians starter Fausto Carmona, who gave up just one run on four hits in 7 1/3 innings.
Harang, who issued an intentional walk and had five strikeouts in a 101-pitch effort, left the game with the score tied at 1.
"He's going to get wins," said Baker. "When he gets them, they'll come in bunches. Right now, we're getting wins. That's what is important."
Ben Francisco's first home run of the season off David Weathers put the Indians ahead, 2-1, in the eighth. But the Reds rallied back to prevent Harang from enduring yet another difficult defeat.
"Our offense is starting to get things rolling," Harang said. "I just kept plugging along. Everybody's pitching in and doing their part. I enjoy pitching in close games like this. It's mentally draining. You really have to focus."
Ryan Garko's RBI double with one out in the second inning put the Indians ahead, 1-0.
Following Brandon Phillips' two-out single in the first, Carmona retired the next 10 batters he faced.
The Reds managed to hit just three balls out of the infield against Carmona in the first five innings.
Their only notable scoring threats were in the first, when they had runners on first and second with two outs, and fifth when Encarnacion led off with a single but was left stranded at third.
Harang, meanwhile, scattered five hits through five innings.
The Reds tied the score in the sixth. Jerry Hairston Jr. doubled to left with one out, and advanced to third on a wild pitch. After Ken Griffey Jr. grounded out, Phillips laced a single to center to drive home Hairston with the tying run.
Bill Bray (1-0) pitched a scoreless ninth to earn the victory.
Kobayashi (2-1) suffered his first blown save of the season and took the loss.
Dunn's game-winning homer narrowly missed exiting the ballpark, landing in the final row. While he's come close on a few occasions, Dunn has yet to hit a ball out of Great American Ball Park.
"I don't care anymore," Dunn said. "That's for the younger guys. I'm done trying to hit it out of here."