Harang, for the second time in as many starts, tied a career high with eight earned runs allowed. He gave up seven hits, including three home runs, in a season-low 3 1/3 innings as the Cardinals rolled to a 9-3 victory before 30,713 fans at Great American Ball Park on Saturday night.
Albert Pujols homered twice for the Cardinals, who improved to a National League-leading 37-28 on the road in extending their winning streak to four games.
The Reds, meanwhile, stretched their home losing streak to eight games, their longest streak since losing nine straight at Cinergy Field in 2001.
"It ain't fun right now," said Harang. "I feel like I'm letting the team down. I don't have any control of my offspeed stuff. My fastball's flat. Something's off, but I don't know what. I have to figure out what it is."
In his previous outing, last Sunday, his first since being reinstated from the disabled list, Harang gave up eight earned runs on nine hits in four innings in a 13-4 loss to Houston.
Despite missing nearly a month with a forearm strain, Harang still insists he feels fine physically. But his struggles extend beyond that injury. In his past three starts, he's 0-3 with 22 runs allowed in 11 2/3 innings.
Harang (3-13) walked three and struck out four on Saturday.
Reds manager Dusty Baker says he's more concerned with Harang's mental well-being than his velocity.
"It's just a matter of command," Baker said. "He's throwing the ball 90 mph. I'm concerned about his psyche. He's not used to getting hit like this. You need location and movement to be successful. I'm worried about his confidence at this point."
Saturday's game started well for Harang, who retired the Cardinals in order in the first inning.
The Reds grabbed an early lead when Brandon Phillips' sacrifice fly scored Jerry Hairston Jr. in the bottom of the first.
In the second inning, however, things again unraveled for Harang.
Yadier Molina's bases-loaded single to left tied the score at 1. The Reds were unable to complete a potential inning-ending double play on Aaron Miles' slow roller, allowing Troy Glaus to score the Cardinals' second run. Moments later, Skip Schumaker launched an 0-1 pitch from Harang onto the lawn past the center-field wall for a three-run home run, giving the Cardinals a 5-1 lead.
The Reds had the bases loaded with one out in the second, but did not score. St. Louis made them pay when Pujols' belted his 25th home run in the third inning to make the score 6-1.
Following a two-run homer by Ryan Ludwick in the fourth, Pujols belted his 26th round-tripper to give the Cardinals a commanding 9-1 lead. It was Pujols' 23rd career multihomer game and third this season.
The fourth set of back-to-back homers this season for the Cardinals sent Harang to the showers after just 78 pitches.
"After the first inning, things were going well," Harang said. "I don't know what happened after that. I'm going to have to sit down and watch some video. I've never gone through something like this. This isn't a fun period for me right now."
Andy Phillips hit his second career pinch-hit home run in the fifth to make the score 9-2. It was the third pinch-hit homer this season for the Reds.
Brandon Phillips hit his 19th home run on the first pitch from Cardinals starter Joel Pineiro in the sixth.
Pineiro (6-5) allowed three earned runs on seven hits in six innings. He struck out six and did not walk a batter.
Josh Fogg, who was scheduled to make his next start on Tuesday against the Cubs at Wrigley Field, allowed one hit in two scoreless innings of relief.
As a result of his relief stint, Baker said Fogg's start tentatively has been pushed back to Friday in Colorado.
With a nine-game road trip upcoming, Baker is concerned about the overall condition of his bullpen.
"There's been a definite strain on the bullpen," the manger said. "They're going to get worn out soon, if they're not already."