In that Game 6, Oswalt held the Cardinals to a run on three hits in seven innings, pitching Houston to its first pennant.
On Saturday night, Oswalt takes the hill in another NLCS Game 6, but the circumstances surrounding this start are profoundly different. Oswalt will be pitching not to send his team to the World Series, but to keep it alive, to even the series at three and push the NLCS to a Game 7 for the first time since 2006.
The five years that separate the two starts include Oswalt's transition from a power pitcher to more of a finesse one -- a 33-year-old veteran who, according to manager Charlie Manuel, has more weapons at his disposal now.
Saturday is also a moment for which Oswalt has waited a long time. He claims to treat every game as a must-win, but even he admits this one is particularly important.
"You never know what you're going to get back here," Oswalt said, reflecting on how difficult it has been for him to reach the postseason after that 2005 season in Houston. "I don't know how much longer I'm going to play. I may not get to this spot again. So I'm going to try to do everything possible to get to that final game."
It was that sense of urgency that compelled Oswalt to march down the right-field line to the Philadelphia bullpen in Game 4, making himself an available reliever despite throwing his bullpen session earlier in the afternoon. His selfless gesture was commendable, but it also earned him the first loss of his postseason career, when Juan Uribe lifted the game-winning sacrifice fly to left field.
Oswalt maintains that those extra 18 pitches thrown in the ninth inning on Wednesday night won't affect him on Saturday.
"I don't think it's going to hurt him at all. I think when he tells you he's ready, I think he's ready," manager Charlie Manuel said. "I trust him. I trust him a lot."
Manuel is right to trust Oswalt, whose postseason pedigree and success at Citizens Bank Park since joining the Phillies are hard to ignore before a game of this magnitude.
Even with Wednesday's loss added in, Oswalt is 5-1 with a 3.58 ERA in 11 postseason appearances. He has been even better in the NLCS, going 3-1 with a 2.93 ERA in six games. He was the 2005 NLCS MVP, and his team has never lost a game he has started in this round.
Those numbers, though, aren't as good as his stats pitching in Phillies' pinstripes at Citizens Bank Park this season. Oswalt made six starts at home since joining Philadelphia, winning five of them and posting a 1.76 ERA. And that's not exactly a new development. In his career, Oswalt is 9-0 at the stadium with a 2.10 ERA in 10 starts. His team has never lost a game he's started in this park.
"You've got your fans with you, and everyone feels comfortable here," Oswalt said of pitching at Citizens Bank Park. "I think the excitement of the crowd and adrenaline gets you going a little bit at home more than it does on the road, and when you get into an environment on the road, one little thing they get going and it seems like they build off of it. Same thing here at home. If we get a hit, fans get into it, hitters start believing, they all feel like they can get a hit. And it just kind of escalates from there."
You might be able to tell that Oswalt doesn't solely subscribe to the baseball platitude that momentum is only as good as tomorrow's starter. He acknowledges that it can play a big role in turning a lineup over, in sparking a dormant offense, and in lifting a team that was down for games at a time.
However you define momentum before Game 6, though, it appears to be on Philadelphia's side. Coming off a come-from-behind win against San Francisco's ace in Game 5, the Phillies can now lean on a pitcher who has been there and done that. And Oswalt knows how to handle this stage.
"You always have adrenaline when you go out there, especially games like this," he said. "But I think after you have over 300 starts in the big leagues you still try to treat it as another start, and you don't try to get caught up in too much of the hype of it. Treat it like another ballgame, and try to do what you normally do when you go out there."
Tim Britton is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.