Admitting to "a little bit of nervous adrenaline," Harang left too many fastballs up in the strike zone and allowed seven hits and seven runs in three innings to a Reds lineup minus many projected starters.
"You kind of want to go out there and do well against your old team," said Harang, the Reds' opening day starter the last five seasons who signed with his hometown Padres in December. "I guess I look at it that it's better to get it out of the way down here than having it happen the first time throwing against them during the season.
"They came out swinging. They knew I was going to throw strikes. Them knowing my history, that I'm not going to back down, I'm going to come right at you with the fastball, they were taking advantage of it with the ball being elevated and swinging at the first pitch."
The 6-foot-7 Harang spent the last 7 1/2 seasons with the Reds, winning 16 games in 2006 and 2007. But he struggled the last three years, going 6-7 with a 5.32 ERA in 2010, when he was bothered by back spasms.
After retiring the first three batters to run his spring streak to nine straight, Harang allowed five straight hits to open the second inning, including Hanigan's homer.
Harang (0-1) had trouble out of the stretch.
"Out of the windup I was good," he said. "The last start everything was down in the zone. The first inning it was down in the zone. I just got out of the stretch and I got a little ahead of myself and was staying elevated. It always equates into bad situations. But it's only my second start, so we're not too worried about it. It gives me something I've got to work on in my next bullpen and future starts."
After giving up five runs in the second inning, he started the third inning in the stretch, but walked Yonder Alonso and then gave up Heisey's homer.
"The first inning he threw some good pitches," manager Bud Black. "Actually his last eight to 10 pitches were pretty good in the third inning. In between, just too many balls mid-thigh to the belt. That's what spring training's for. You've got to resolve this. He's going to be fine."
Juan Francisco hit a two-run homer in the sixth off Matt Lollis.
"It was their turn today," said Cincinnati manager Dusty Baker, whose Reds took a similar pounding on Monday, losing 11-3 to Kansas City.
Edinson Volquez had been scheduled to start for Cincinnati, but returned to the Dominican Republic to straighten out a work visa issue. He was due back in Arizona later Wednesday.
Chad Reineke (2-0), who was with the Padres briefly in 2008, allowed just a walk in two innings.
"We played well. We pitched well. We played a heck of a defense," Baker said. "Especially when those young boys got in there they were all over the place. The (young players) are hard to pitch to. If they can hit the fastball, they're going to hit."
San Diego's Casey Kelly, the key prospect obtained from Boston in the Adrian Gonzalez deal, pitched two perfect innings. He hasn't allowed an earned run in five innings spanning three appearances.