It took 4 hours, 34 minutes and 15 innings to play, but the D-backs will take it as they came away with a 2-1 win at Great American Ball Park.
Nick Ahmed's two-out single to left-center in the 15th proved to be the game-winner.
"I wanted to be aggressive," Ahmed said. "I knew hopefully I was going to get something to hit and was just looking for something I could do some damage with in the middle of the field and drive him in. I was just looking to hit the ball hard and I got a good pitch to hit and put a barrel on it."
Martin Prado started the rally when he drew a one-out walk from J.J. Hoover, who was in his second inning of relief.
Prado moved to second on a groundout to first baseman Brayan Pena by Didi Gregorius and he came around when Ahmed drove his single to left-center.
"That ball was just far enough away from Pena where he couldn't stay on his feet and get the lead runner at second base or they probably don't score that inning," Reds manager Bryan Price said. "That's the way it is. You can't hold guys down for 15 innings. Somebody is going to score. It's unfortunate to waste that type of pitching. It really is."
The hit made a winner of reliever Oliver Perez (1-1), while Hoover fell to 1-8.
Both starting pitchers probably deserved a win for their efforts, but were long gone when the game was decided.
D-backs rookie Chase Anderson allowed one run on three hits while matching a career-high in strikeouts with eight over his seven innings of work.
"The pitchers have been great," Ahmed said. "The bullpen was lights-out and Chase threw a great game tonight, so it was good to come through and pick those guys up, because they've been doing an outstanding job the last few weeks."
Reds right-hander Homer Bailey allowed one run on five hits in eight innings.
The Reds got on the board first when Devin Mesoraco led off the second inning with a home run to left.
It looked like the Reds might add on during the inning when Pena doubled with one out and Kristopher Negron followed with a single to center.
Cincinnati third-base coach Steve Smith waved Pena home on the single and Ender Inciarte's throw to the plate easily nailed Pena.
"Chase threw the ball really well," Montero said. "He hit his spots pretty well today. He made one bad pitch and he gave up the homer. In this park, you can't make many mistakes. Other than that, he threw the ball well. He kept the ball down, was working ahead in the count and mixing speeds. He was pretty good."
The D-backs tied the game in the fourth when Mark Trumbo doubled to right-center and Montero followed with a single off the right-field wall.
It was not a night for offenses as the Reds fanned 18 times and the D-backs 12 while both teams managed a combined 14 hits over the 15 innings.
And once the game went to extra innings, players on both sides swung a little harder trying to hit the ball out of the park.
"It was just a long game," D-backs manager Kirk Gibson said. "Great pitching on both sides. We just kept pushing. You don't score, you get into games like this and everybody's trying to end it. You try to tell yourself not to do it but the reality of it is, that's what happens. We hung in there and got the win."
As players showered and dressed after the game, Gibson told them he was cancelling batting practice for Tuesday and he did not want players showing up early as they usually do. Instead, he said, they should get some extra rest and ride the team bus over at 1 p.m. MST, for the 4:10 p.m. game.