The Phillies' No. 11 prospect continued his impressive August on Tuesday, tossing a three-hitter for his first career shutout as Triple-A Lehigh Valley beat Toledo, 1-0.
Since giving up two runs on five hits over five innings in his International League debut on July 30, Pettibone (4-0) has won four consecutive starts while holding opponents to one run or fewer in three of them.
The transition from the Eastern League has been a seamless one for the 22-year-old right-hander, who attributed much of his Triple-A success to an expanded repertoire.
"Early on, I was mostly just going fastball [and] changeup, and that got me through the first couple of outings," Pettibone said. "When I was promoted last month, I was introduced to the cutter. I worked it in over my first couple of starts here in Triple-A and today I switched to it later in the game and it really took off inning by inning. And by the end, it was a key pitch for me."
While he has worked to vary his pitches since arriving in Lehigh Valley, Pettibone has been sure not to stray too far from the framework he's built for himself, most recently at Reading. He was 9-7 with a 3.30 ERA in 19 starts for the Phillies' Double-A affiliate.
"I think the biggest thing was just keeping the same approach," the 2008 third-round Draft pick said. "But I also [realized] that I was at a higher level and I had to make better pitches. I think one thing I found that I struggled with was that I was trying to be too fine with everything, I started falling behind in counts or walking guys.
"Down in Reading, I was an aggressive pitcher, attacking the zone and throwing first-pitch strikes. The biggest thing that I have to do mentally is just keep the same approach, get ahead of hitters and go from there."
Tuesday was the third straight start in which Pettibone has gone seven innings. He blanked Syracuse on two hits on Aug. 10, then allowed a run on seven hits against Buffalo on Aug. 15. He has a 1.69 ERA over 32 innings at the Minor Leagues' highest level.
As the final weeks of the season wind down, Pettibone said he's aware of the effects overthrowing can have on a young arm, especially one that's already pitched 149 1/3 innings this year -- more than any other Lehigh Valley pitcher. Staying healthy will be his primary goal.
"Other than that, pitching-wise, I want to continue to develop that cutter," he said. "I've only thrown it for a few starts and I want to be confident with it by the offseason, going into next year."
Toledo starter Casey Crosby (7-7) made just one mistake, allowing a second-inning homer to Cody Overbeck. It was one of six hits the Tigers' No. 3 prospect yielded while striking out four over six frames.