[caption id="attachment_42599" align="alignright" width="300"] Jonathan Pettibone has been a revelation for the Phils. But how long can it continue? (AP Photo).[/caption] As I wrote in my recap on Tuesday night, Jonathan Pettibone deserves a lot of credit. He has started five games so far this year and the Phillies have won four. He has shown a veteran's ability to battle through jams. He has displayed a pretty good fastball, which at least through his first three starts, he routinely threw for strikes and forced opposing batters to put the ball in play. But before we all get carried away, it's important to note that Pettibone is not the first marginal Phillies pitching prospect in recent years to enjoy immediate success upon his big league promotion. Consider the statistics for the following Phillies starters, past and present, compared to Pettibone through five starts: Jonathan Pettibone: 3-0, 3.41 ERA, 1.28 WHIP, 5.3 K/9 in 29 IP Vance Worley: 2-2, 2.09 ERA, 1.11 WHIP, 7.7 K/9 in 27 IP J.A. Happ: 1-1, 3.57 ERA, 1.30 WHIP, 6.5 K/9 in 27.2 IP Kyle Kendrick: 3-0, 4.40 ERA, 1.42 WHIP, 2.9 K/9 in 30.2 IP While the numbers are different, each former farmhand was able to have a certain level of success right away. Pettibone’s rookie predecessors were also able to sustain their effectiveness beyond their first start. Worley was a huge part of a playoff team in 2011. Ditto for Happ in 2009 and Kendrick in 2007. But each pitcher’s success came to an abrupt end after one season’s worth of starts… or about the amount of time it took for the majority of the league to get another look at them. For the most part, that is what happens with mid-level pitching prospects that are, at best, projected to be back-end of the rotation starters. And the odds are, it will likely happen with Pettibone too. I point this out not to throw cold water on Pettibone’s promising start, but simply to temper the expectations on a pitcher who has displayed guts, but only mediocre stuff. Anytime a prospect comes up and hits the ground running, it is easy for fans to excitedly pencil him into the lineup or rotation for the foreseeable future. Hell, it is easy for players to do it too. Here is Kevin Frandsen on Pettibone after Tuesday’s performance, courtesy of Mandy Housenick of the Allentown Morning Call: "He never gave in. He could have let it go when we were down 2-1 and he kept fighting and fighting and made great pitches. … That's a stud right there. He didn't back down. That's awesome." Pettibone has certainly been resilient and shown a comfort level pitching in sticky situations. And it is great that his teammates are excited for him. But what Frandsen sees as moxie, I see as a caution sign. Although he has battled out of them, Pettibone’s been in those jams for a reason. His WHIP of 1.28, while not bad, indicates that his ERA is due for a correction. And after issuing four free passes in each of his last two starts, his walk rate is headed in the wrong direction. While Phillies Nation graded Pettibone as the organization’s sixth best prospect headed into this season, that ranking needs to be taken with a grain of salt in the grand scheme of things. The Phillies farm system has been decimated by trades, and – Domonic Brown’s development excluded - hasn’t produced a single impact player in more than five years… an assessment that stands even if you count the top prospects they’ve traded. Given the history with Phillies pitchers of his ilk, it is possible, and maybe even likely, that Pettibone’s effectiveness continues well into the summer. Credit him for working hard to get this far... and credit Rich Dubee for getting these guys acclimated to the big leagues so quickly. Just don’t bank on it lasting. While Kendrick has miraculously transformed himself from a Pettibone-type into a trustworthy middle of the rotation starter, it took him several years and countless ugly starts to do it. He is the exception.