He also said he "probably won't run around the bases" during BP before Monday night's crucial game.
"I can't be any more careful, anyway," Pettitte said. "While I'm running around, I'm watching the whole time. I jumped out of the way and it still got me. It was chasing me. I couldn't get away from it."
Pettitte took a pain-killing shot so he could start Game 1, and he's done some icing and stimulation therapy in the injured spot since then "just to move the blood out from one area throughout my leg," he said.
But it didn't make him change his between-game routine, Pettitte added.
"I was able to do my stuff in between -- threw my 'pen on the second day like I normally would and stuff like that," Pettitte said. "I've been able to run around out in the outfield the last couple of days like I normally do. I wasn't able to lift my legs the day after, obviously, but that's really no big deal. That was really the only thing that hindered me."
Though Pettitte insisted that the injury didn't affect him, the Cards led 2-0 in the first inning by virtue of Reggie Sanders' two-run homer, and they extended the lead to 5-0 through five innings against Pettitte on their way a 5-3 victory. Pettitte worked six innings, allowing five runs on eight hits with two walks and two strikeouts. His trademark sinker didn't have any bite and he struggled putting pitches in the strike zone.
He appeared sluggish, consistently falling behind in the count against the patient Cardinals hitters.
Astros manager Phil Garner didn't dismiss the fact that Pettitte had struggled on Wednesday because of the knee injury, and he reiterated that assertion on Sunday. Coming into the game, Pettitte hadn't allowed more than three runs in an outing since June 14.
"I think it affected him a little bit," Garner said. "And to his credit, he doesn't make excuses and he's his own worst critic. He's very critical on himself and that's one of the reasons he's great. He will take responsibility and he'll do something to make it better. But I wouldn't say that start was a total disaster, let's put it that way."
In any event, Pettitte, who was tossing only his second playoff game in two seasons with the Astros after making 30 postseason starts in nine postseason appearances with the Yankees, couldn't control the defending National League champions, who outdistanced the Wild Card-winning Astros by 11 games this past season to win the NL Central.
"I was just bad," Pettitte said on Sunday, sounding the same theme as his postgame comments on Wednesday night. "I threw a lot of balls right in the heart of the zone. They took full advantage of them when I did. So just mechanically, I never really got in a real good rhythm, and that's what you'd like to do as a starting pitcher."
Pettitte had elbow surgery during the 2004 season and missed the Astros' postseason -- a five-game NL Division Series victory over the Braves and a seven-game loss to the Cardinals in the NLCS.
But this year he came back with his old flair, finishing 17-9 with a 2.39 ERA, and was the winning pitcher against the Braves in Game 1 of the NLDS. It was the 14th postseason win of his career, second to Atlanta's John Smoltz, but his first playoff win as a member of the Astros. Teammate Roger Clemens is third after the right-hander won his 12th postseason game on Saturday.
Pettitte pitched numerous key postseason games during his tenure with the Yankees from 1995 to 2003. The Yankees qualified for the postseason every year Pettitte was there, went to the World Series six times and won four of them, including three in a row from 1998 to 2000.
He's now 6-2 lifetime in League Championship Series play and 3-4 in the World Series, including the loss in Game 6 of the 2003 World Series when the Marlins clinched the championship at Yankee Stadium and Pettitte pitched his last game for the Yankees.
That evening, Pettitte pitched seven innings of six-hit ball and allowed only one earned run, but Florida's Josh Beckett bettered him with a complete-game five-hitter in a 2-0 Yankees defeat. Less than two months later, Pettitte signed as a free agent with the Astros.
Game 5 on Monday now will be his biggest game since then.
"No matter what happens, it's all the same," Pettitte said. "This is the postseason. I'm not going to be successful unless I get out there and get in a good rhythm, get in the zone, move the ball around and change speeds. That's what it's all about -- making pitches. No matter what happens, I will not change my approach in any way."