The 37-year-old Carpenter had surgery in July for a nerve problem that left his throwing arm and much of the right side of his body numb. He came back on Sept. 21, and is 0-2 with a 3.71 ERA in three starts.
"Everybody knows that it wasn't supposed to happen," Carpenter said about the prospect of pitching at all in 2012. "I put a lot of work into it, to hopefully have this opportunity. I didn't know if I was going to have this opportunity or not and fortunately, I do."
He is 9-2 with a 3.05 ERA in the postseason for his career.
That includes going 4-0 with a 3.25 ERA last year while helping St. Louis win the World Series; he beat the Texas Rangers in Game 7 for the title.
"Him winning the World Series last year or whenever isn't going to do anything for him tomorrow," Nationals third baseman Ryan Zimmerman said. "He's a great pitcher, and nobody's taking anything away from him in that aspect, but tomorrow we're going to go out there with our plan and try and do what we've done all year."
Which was good enough to own the best record in the major leagues at 98-64.
Strasburg played a key role up until his final start, a three-inning outing on Sept. 7. The No. 1 overall pick in the 2009 amateur draft went 15-6 with a 3.16 ERA with 197 strikeouts in 159 1-3 innings.
General manager Mike Rizzo made quite clear all season that his prized right-hander's innings would be limited in his first full season back from Sept. 3, 2010, reconstructive elbow surgery.
"I bet the kid has to be going crazy, being in the situation where he is," said Cardinals right fielder Carlos Beltran, who hit two of his team's four homers Monday in Game 2. "He pitched all regular season, and right now he's not available for them."
Unable to put Strasburg on the mound now, the Nationals used playoff rookies Gio Gonzalez and Jordan Zimmermann in Games 1 and 2.
"The starting pitching, we showed a little inexperience there," manager Davey Johnson said. "I mean, not going right after hitters and also not pitching."
Washington now needs to rebound from that 12-4 loss in Game 2 at St. Louis, although the Nationals prefer to focus on having taken one of their two road games at the outset of the series.
Going up against Carpenter will be his former teammate Jackson, the only starting pitcher on Washington's roster who ever had participated in a playoff game before this season. He was a member of the Cardinals' championship club in 2011, and his overall postseason mark is 1-1 with a 4.91 ERA.
He went 10-11 this season, but Washington's record in Jackson's starts was only 12-19.
"It's high expectations on me. I have high expectations on myself, as well," the right-hander said. "This is one of those games where you go out and you try to lead by example."
That's certainly the sort of thing the Cardinals expect from Carpenter, who won the 2005 Cy Young Award and helped St. Louis win a title the following year.
His mere presence on the diamond Wednesday is a big deal to his teammates.
"I saw that first hand, all the time he spent in the training room and weight room and getting back to the point, and you can't help but feed off that," said Cardinals center field John Jay, who made a spectacular wall-crashing catch in Game 2. "Especially a guy (who's) been there before. It would have been easy for him, as someone who has two rings and he's made his money in this game, to say 'You know what? I'll be back next year.' But he wanted to be out there for us."
Strasburg would certainly prefer to still be pitching for Washington.
But Rizzo said Tuesday "there's no sense of thinking" about that possibility at this point.
"We love the pitching staff we have. It's the best pitching staff in major league baseball, with and without Stephen," Rizzo continued, standing near the red-white-and-blue postseason logo painted on his ballpark's grass for the first time, "and these are the guys that we have in the playoff series, and we're going to go forward with them."