The Cardinals, in control of the National League Central all the way en route to a 105-victory season, are in the unfamiliar territory of having their backs to the wall.
The Astros, who played with a sense of desperation the entire month of September and needed the stars to align just right to reach the postseason party, are suddenly in the driver's seat.
And as it headed to St. Louis for Game 6 on Wednesday, the National League Championship Series became a dramatically different beast than it was just a few days earlier.
After the teams traveled from the Bayou City to the Gateway City and used Tuesday as a workout day, the Cardinals will turn to Matt Morris to help them avoid elimination on Wednesday. Meanwhile, the Astros will go with Game 2 starter Pete Munro, leaving Roger Clemens available for a Game 7 start on Thursday, if necessary.
"Because I'm starting Pete doesn't mean we've giving this game away," Astros manager Phil Garner said Tuesday. "It doesn't mean that we are not taking this game as seriously as we've taken any game we've played the last two months."
Capping it off with a 3-0 walk-off win on Monday night, Houston took all three games at home to take a 3-2 series advantage, putting the Astros one victory away from their first World Series berth.
Just don't tell them that, because they know that one victory is a big one, and it won't be even remotely easy.
"I'm not even talking about the World Series right now," Astros catcher Brad Ausmus said. "We've got a game Wednesday."
After winning their 22nd home game in their last 23 tries, the Astros will be heading into a place the Cardinals made quite the home-field advantage for themselves, winning a National League-high 53 games in front of the red sea of fans at Busch Stadium.
Added Jeff Bagwell: "We realize we're playing a helluva team and we're going to their place to play."
On the flip side, the Cardinals didn't win all the games they won this regular season and then march through the Dodgers in the Division Series by backing away from challenges.
Matt Morris / P
Weight: 220 lbs
Bats: R / Throws: R
Despite three losses in three different, but equally frustrating ways, the Cardinals are not exactly packing their bags for the winter. This team has been aiming for the World Series, and that goal is still within their reach.
"There hasn't been on situation this team faced where I haven't liked our chances," Cardinals manager Tony La Russa said. "I really like the club. I know we'll be ready Wednesday. We understand that we have to win the game to play on Thursday.
"So, yeah, I like our chances and I love our club."
As superstar slugger Albert Pujols noted after Monday's loss, it takes more than three victories to clinch the National League pennant.
"We've been playing great at home," Pujols said. "I don't think it's over until you win four games. The only difference is we need to win two games and they need to win one."
Roger Clemens / P
Weight: 235 lbs
Bats: R / Throws: R
Even Jason Isringhausen, the Cardinals closer whose final pitch of Game 5 was sent into the bleachers in left field on Jeff Kent's walk-off, three-run homer Monday night, heads to St. Louis with more of a sense of confidence than a sense of tension and urgency.
"Not too many other people get to pitch in this kind of situation," Isringhausen said after Game 5. "It's a lot of fun for me. I enjoy the challenge. Jeff Kent beat me today. But hopefully in the next few days I'll get a chance to beat him, and we'll go at it again."
These are two veteran-rich teams who know there are at least nine innings to go before we know whether this one's over or it's headed for a Game 7. They've faced each other 23 times now in 2004, and they're very well aware that their 24th meeting is likely to bring out the best in both clubs.
They might have switched roles a bit as the series heads to St. Louis, but for either of them to think anything's over would be out of character for both.
"We're not counting what we have in our pocket. We know what else we have to put in our pocket," Garner said. "We have to stay focused, as we've been doing for quite some time now. You just play until this series is over and then you look up and see where you are and where you're headed.
"We've got plenty of work to do. This is a good ballclub, a great ballclub that we're facing -- not good, they're great. We're close, but that doesn't do you any good."
John Schlegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.