"It didn't start good for him," said D-backs manager Kirk Gibson, summing up the evening. "It's a tough start for us and, on the other side of the ball, we didn't have good at-bats when we had opportunities."
It was a rough outing from the get-go as Bauer walked Drew Stubbs to start the game, and an error by shortstop Stephen Drew on a potential double-play ball put runners on first and second.
The Reds pulled a double steal to move both runners into scoring position, and a wild pitch on ball four from Bauer plated Stubbs for an early 1-0 deficit.
Bauer's struggles compounded in the third after a two-batter series that consecutively featured a walk, a botched pickoff attempt, a wild pitch and another walk to put two runners aboard.
"It's pretty obvious, I couldn't throw a strike when I wanted to," said a visibly frustrated Bauer. "I couldn't locate. You put five guys on base and you're going to get beat. It's pretty simple."
After nearly plunking Ryan Ludwick in the head on the first pitch of the ensuing at-bat, Bauer watched the Reds right fielder take a second-pitch changeup 422 feet to the upper deck of left field for a three-run blast and a 4-0 Reds lead.
Bauer left the game after just three innings, his shortest outing to date, with his pitch count at 73.
"Command was the biggest issue and he couldn't get strike one," said catcher Miguel Montero. "He was working up in the strike zone but they never swung at them. I don't know what I can do, you know? I just try to help in some way, but it's just like I'm guessing myself. What pitch should I call to help get him out of the jam. It's tough to catch like that."
Ludwick's home run was the only hit Bauer gave up on the night, but the rookie walked four batters and threw two wild pitches before making an early exit.
The loss marked the third time in four starts that Bauer has failed to last past the fourth inning.
Bauer, who zoomed through the Minor Leagues after being selected third overall in the 2011 First-Year Player Draft, entered Tuesday's game on the heels of his best Major League outing yet, allowing just two hits to the Dodgers in six innings.
"The young man over there has outstanding stuff," said Reds' manager Dusty Baker. "He was just all over the place and couldn't find the plate, which helped us."
Bauer has shown glimpses of the potential he has in store, but called Tuesday's showing "just one of those days where I couldn't locate."
"I just couldn't throw the ball where I wanted to," Bauer said. "I'll fix it. I'll be fine."
Bauer didn't receive much help from the other side of the ball either, with the D-backs offense failing to record a hit off Reds' starter Johnny Cueto until the fourth inning.
The D-backs eventually strung together two threats, loading the bases in both the fifth and sixth innings, but left both frames empty handed.
"He's got good stuff," Gibson said. "He moves it around. He throws the ball where he wants to throw it. It makes it all that much more important to not give those guys free passes and not make those mistakes and on our side of the ball, having good at-bats."
The D-backs left 12 runners on base in the contest and out-hit the Reds, 8-5, but weren't able to get the crucial hit to drive a run home.
"It's a lot of men left on base," Montero said. "We've got to be better and get our pitch. We couldn't put a good swing on it when we needed it."
The D-backs have scored just 40 runs in July, ranking them in the bottom five in the league.