Corbin lasted just five innings and allowed five runs on nine hits while Petit struck out a career-high 10 batters as the D-backs fell, 8-2, to the Giants at Chase Field and remained six games back of the Reds for the last NL postseason spot.
"I felt all right, just wasn't really locating anything," said Corbin, who struggled his last time out as well, surrendering eight runs over 5 1/3 innings vs. the Phillies.
There was a time this season when it looked as if Corbin might begin his sophomore season as the D-backs' No. 5 starter and end it hoisting the NL Cy Young trophy. That sort of talk comes with the territory when a pitcher brings a 12-2 record and a 2.24 ERA into August.
But with his ERA over his last six starts ballooning to 5.63 and after he failed to work at least six innings in consecutive outings for the first time all year Sunday, the 24-year-old had to answer the inevitable question of whether his remarkable season is simply running out of gas.
"My arm feels great; I pitched this late into the season last year, I feel great," he said. "It just hasn't been my day the last few starts. I know it's just baseball but it's tough. I'll try to get better next time."
Corbin worked 186 1/3 innings in 2012 between the Minors and Arizona, and after Sunday, he is at 182 2/3 innings in 2013. But although those totals are fairly close and one would assume normal progression would allow him to throw more innings this year, D-backs manager Kirk Gibson thinks it's a different beast spending an entire year in the Majors.
"Who's not tired? Everybody is fatigued," Gibson said. "But it's the first time he's gone through it in the big leagues, so I'm sure it's something he'll learn from. He's trying; it's not like he's throwing it terrible."
Armed with an early lead Sunday after Martin Prado put the D-backs ahead with a two-out RBI double in the first, Corbin first ran into trouble in the second inning when a leadoff walk to Hunter Pence came around to score on Hector Sanchez's RBI groundout following a Pablo Sandoval sharply hit single to right field.
The lefty seemed to settle down the next inning when he struck out two and retired the side in order, but that momentum didn't last long.
After Corbin served up a single and double to put himself in a second-and-third, nobody-out jam in the fourth, he sat down the next two Giants batters in order to move within one out of escaping the inning with the scored still tied at 1.
That, however, is when Corbin's afternoon fell apart.
Ahead 1-2 in the count on Sanchez, who entered the game batting .243 this season, Corbin threw a slider that caught too much of the plate, and the Giants catcher ripped it into the left-center-field gap for a back-breaking two-run double.
"I think it was up a little bit. I should've buried it," Corbin said. "It should've been a pitch that he probably couldn't have even touched. I just left it up. I feel like I did that quite a bit today."
Said Gibson, "He should've bounced that ball. His breaking stuff was doing that all day. He couldn't get it all the way in and everything kind of ended up out over the plate."
Two batters later, Corbin compounded the damage when his counterpart, Petit, drove an RBI single into right field to put San Francisco ahead 4-1. The Giants tacked on one more run off Corbin the following inning on Pence's 17th homer of the year.
"He's a great pitcher and we were able to get some hits when it counted," Pence said. "But he has electric stuff. That's why he's having the success he's had this year."
Offensively, Sunday was just as perplexingly substandard for the D-backs' lineup, which figured to be poised for a productive afternoon facing Petit, who spent three years with Arizona from 2007-2009 and has never experienced much success in the big leagues. Instead, the D-backs never could come up with the big hit, struggling to put the ball in play and finishing just 1-for-8 with runners in scoring position.
"When you get guys on base, you have to drive them in and when you don't do that, you aren't going to be very successful," Adam Eaton said. "That's baseball."
Petit finished his day limiting the D-backs to two runs on seven hits over six-plus strong innings.
"He just had a good gameplan, he threw a lot of strikes, elevated his fastball then threw a good chase curveball," Gibson said. "I just don't think the guys were picking him up well at all."