How Andy Pettitte went about defying age this season

You can bet on the following: Death. Taxes. The sun rising. And Andy Pettitte coming up big in a big playoff game.

It was only a single game, but with his 7-inning, 2-ER, 88-pitch performance against the Twins, it looks as though Pettitte has regained the All-Star form he was showing before he injured his groin mid-season. This is, of course, a huge development for the Bombers, who now boast a 1-2 punch as good as any playoff team’s, and an offense that has gotten contributions up and down the lineup so far against Minnesota.

Fans of All Day AP know that a solid October performance is nothing new from the big Texan lefty, but lost amid all the stories of his resurgent season and subsequent injury was a simple question: Where did this dominance come from?

Even with his three sub-par rehab starts harming his season numbers, Pettitte posted a 130 ERA+ this year, his best AL performance since 2002, and an improvement upon his career ERA+ of 117 and last season’s 111. Some of this may be luck, as Pettitte’s 3.28 ERA and 3.85 FIP suggest, but Pettitte improved his line across the board this season from last. Take a look:

These numbers demonstrate just how much Pettitte improved from 2009 to 2010, albeit in a truncated season. The major differences appear to be in Pettitte’s walk rate and his ability to strand runners. He’s giving up fewer passes, and that may be translating directly into getting out of trouble more quickly. That has shown up in his ERA, but he has also improved his FIP and xFIP. Big Game Andy Pettitte has pitched better in 2010, across the board.

Interestingly, he hasn’t tinkered much with his approach from last year. He’s throwing roughly the same mix of pitches:

All data are from Fangraphs.

Apart from the increase in the unknown pitch, Pettitte has barely changed his method from 2009. He is throwing slightly more curves, and slightly fewer changeups, but that’s it. He’s throwing the same proportion of fastballs and cutters, and his velocity is essentially the same (and down a bit, if anything). But the results are almost improved across the board:

Andy’s best pitch remains his cutter, but that is actually worse this year. Its velocity and effectiveness are down, slightly. It’s Pettitte’s other pitches that are improved. His fastball and changeup are almost neutral pitches for him this season, while his curveball is more effective. The combination has been devastating, as the numbers indicate. While last season Pettitte would have needed to keep his fastball and change away from hitters to set up his out pitches, this season he can safely challenge guys more with the straight stuff, better setting up his breaking pitches. The big question — what led to this age-38 across-the-board improvement? — remains a mystery.

What is certain is that, to the extent you trust one lights-out performance against one of baseball’s top offenses, Pettitte may have become the biggest October development for the Yankees, and perhaps for 2011. CC Sabathia-and-pray-for-rain is one playoff pitching strategy, but the Ace and Ace-1A strategy of Sabathia and Andy Pettitte is better. The Yankees’ ability to make a deep run in October always rested on Pettitte’s broad shoulders. His ability to shoulder that load is certainly now less in doubt. This has implications moving forward in October, but also for next season. If Pettitte’s start against Minnesota wasn’t a one-time event (it wasn’t) then re-signing him will once again become a key element to the Yankees’ offseason plans once the playoffs are over.