Now comes Game 6 of the World Series on Wednesday (6:30 p.m. CT air time on FOX, 7:07 p.m. first pitch) at Boston's Fenway Park, with the Red Sox leading, 3-2, in the Series and the Cardinals on the brink of going home.
Does the 22-year-old Wacha have one final gem left in that rookie right arm?
"I'm going out there to try to keep the season alive," Wacha said. "It's must-win from here on out. That's the mindset going in there: win a ballgame."
The wins have been plentiful, beginning with Wacha's near-no-hitter against the Nationals in his final start of the regular season that cemented his spot in the Cardinals' postseason rotation. With the team facing elimination in Game 4 of the National League Division Series against the Pirates on enemy turf, Wacha didn't allow a hit until Pedro Alvarez's home run with two outs in the eighth inning of a 2-1 Cards win. In the NL Championship Series against the Dodgers, Wacha twice outdueled Clayton Kershaw, scattering seven hits in 13 2/3 scoreless innings, including a seven-inning clincher in Game 6 that sent St. Louis to the World Series and made Wacha the NLCS MVP.
The Red Sox made Wacha work in Game 2, pushing him to a career-high 114 pitches, but he limited the damage to three hits and two runs and was rewarded with another win when Sox reliever Craig Breslow aired a throw past third base amid the decisive Cardinals rally.
Add it all up, and this is historic stuff:
Michael Wacha's past five starts, including his regular-season finale against the Nationals
• Wacha is 4-0 with a 1.00 ERA in his October starts, the 17th pitcher in history to win at least four games in a single postseason and the first since teammate Chris Carpenter in 2011. Only two pitchers have won five times in a single postseason: D-backs starter Randy Johnson in 2001, and Angels reliever Francisco Rodriguez in 2002. Both of those players' teams won the World Series.
• Wacha worked 19 consecutive scoreless innings between Alvarez's home run in the NLDS and David Ortiz's two-run homer into the Monster Seats at Fenway Park in the sixth inning of World Series Game 1, matching Bob Gibson for the longest postseason scoreless streak in Cards history.
• Opponents are hitting .127 against Wacha this month, the fourth-lowest average in a single postseason against pitchers who logged at least 20 innings. The Orioles' Mike Mussina held opposing bats to a .112 average in 1997, and the Tigers' Kenny Rogers in 2006 and the A's Blue Moon Odom in 1972 each held hitters to a .120 average.
"I guess it's expected now," said Cardinals third baseman David Freese, who knows a thing or two about Game 6 of the World Series. "Man, he's a great talent. He works his tail off. He soaks it all in. And he obviously enjoys the moment."
Game 6 will be the biggest moment yet.
The Cards are trying to do what they did two years ago; stage a comeback from a 3-2 World Series deficit. But in 2011, they played Games 6 and 7 at home against the Rangers. This time, they will have to win Games 6 and 7 on the road, in Boston, where the Red Sox have not clinched a championship since 1918.
Key stat: Wacha is the 17th pitcher in history to win at least four games in a single postseason.
Key stat: Lackey has thrown 5 2/3 more innings in the postseason than Wacha has in his entire career.
At Fenway Park
2013: 1 GS, 1-0, 3.00 ERA Career: 1 GS, 1-0, 3.00 ERA
2013: 15 GS, 7-4, 2.81 ERA Career: 61 GS, 27-22, 4.69 ERA
Against this opponent
2013: 1 GS, 1-0, 3.00 ERA Career: 1 GS, 1-0, 3.00 ERA
2013: 2 G, 1 GS, 0-1, 3.68 ERA Career: 2 G, 1 GS, 0-1, 3.68 ERA
Loves to face: Xander Bogaerts, 0-for-2, 2 K Hates to face: David Ortiz, 1-for-2, HR, BB
Loves to face: Carlos Beltran, 1-for-12, 2 BB, 3 K Hates to face: Yadier Molina, 1-for-4
Why he'll win: Wacha has allowed just three earned runs through 27 innings this October, while limiting his opponents to a .122 batting average.
Why he'll win: Lackey has held his opponent to four or fewer runs in 14 of his 15 career playoff starts. Only Andy Pettitte has more such starts (16) in the American League since 2002.
Pitcher beware: Ortiz snapped Wacha's scoreless streak of 19 innings with a two-run homer in Game 2 and is 11-for-15 with two homers and six RBIs in the Series.
Pitcher beware: Though they haven't hit like it consistently in the playoffs, the Cardinals still boast a dangerous lineup that was fourth in batting average (.269) and third in runs (783) in the regular season.
Bottom line: Since coming within an out of a no-hitter in his last regular-season start, the 22-year-old rookie hurler has turned in one impressive performance after another. The Cardinals hope he has one more in the tank as he makes his second World Series start.
Bottom line: Though Lackey was tagged with the loss in Game 2, he left in the sixth inning when the Red Sox were up, 2-1, and the Cardinals hit just 5-for-24 against him. A repeat performance and some better luck could go a long way toward putting the first blemish on Wacha's October resume.
The Red Sox were on the road when they won the World Series in 2004 and '07, so Fenway Park will be in full party-planning mode on Wednesday.
"I imagine it's going to be crazy," Wacha said, "but I'm not going to pay any attention to it. I'll keep going about my business the way I have been in all my starts this year and not worry about the crowd. And [I'll] just get locked in with Yadi [Yadier Molina] behind the plate and just make my pitches."
Can Wacha do it one more time? And if he does, will the Cardinals think of any other superlatives to send his way?
"What more can you say about this guy?" St. Louis second baseman Matt Carpenter said, and then gave it a shot. "There's so many things that are impressive about this, and we've all heard them -- how young he is, how little experience he has and how dominant he's been thus far.
"But the thing that I really appreciate from him is his humbleness and his ability to work. Those are two things that I always look at people -- how hard are you working, and when success kind of comes your way, how do you handle it? He's handled it very, very well, and that's something that I think is one of the more impressive traits in what he's doing."
Red Sox Game 6 starter John Lackey has an idea of what Wacha is doing. He was an Angels rookie in 2002 who had turned 24 days earlier when he started Game 7 of the World Series against the Giants.
Lackey allowed one run in five innings and was the winning pitcher in the Angels' title clincher.
"I don't know what kind of guy [Wacha] is," Lackey said. "But personally, I was more excited about it than anything else as far as nerves, that sort of thing."
The Cards found themselves in unfamiliar territory on Monday night, having lost consecutive games for the first time since Games 2 and 3 of the NLDS against the Pirates. Wacha is the one who stopped the losing streak in Game 4.
St. Louis has faced a 3-2 deficit in the World Series on six previous occasions in franchise history, and the Redbirds have forced a decisive Game 7 five times.
"I think it starts with a mentality that it's a great challenge," Cardinals manager Mike Matheny said. "It's a great opportunity for us to go in and prove the kind of team we are as far as how tough we are mentally, and I think that's where it begins. After that, it comes down to execution. We've got to have Michael come out and throw a big game."
One last big game.
"We have to win the first game first. Game 6. It starts with that," said Adam Wainwright, who started and lost a hard-fought Game 5. "We have a pitcher in Michael Wacha who we have great confidence in. He's been amazing for us in the postseason, and we don't expect anything less from him going back there.
"This will be legendary if we go into Boston and win two games. It starts with Game 6."
Adam McCalvy is a reporter for MLB.com. Read his blog, Brew Beat, and follow him on Twitter at @AdamMcCalvy. This story was not subject to the approval of Major League Baseball or its clubs.