And with the Red Sox's bullpen taxed after Sunday's 12-inning 5-4 loss, the onus especially falls on Lester to give Boston a long and quality start.
"I think, for both sides, starting pitching will be at a premium," manager Terry Francona said.
Fortunately for Francona's club, Lester, who was not available for comment after the late-night loss, has been a premium pitcher.
"The kid's been good all year," Francona said.
If his first start of the 2008 postseason and his regular season as a whole are any indication, Lester is up to Monday's challenge.
"He's been unbelievable this year," reliever Manny Delcarmen said. "Hopefully he does [Monday] what he always does."
Lester has experience getting the starting nod in potential clinchers. He worked 5 2/3 scoreless innings in Game 4 of the World Series last year to get the win, as the Red Sox swept the Rockies.
Here's the rundown on Lester, who gets the ball with an AL Championship Series berth within reach:
The southpaw went seven innings, allowing just one unearned run on six hits with a walk and seven strikeouts in Boston's 4-1 victory in Game 1. In the regular season, Lester allowed four runs on nine hits in five innings for a no-decision against the Angels on April 23. He is 1-1 with a 7.78 ERA in four career regular-season appearances against them.
At Fenway Park: Lester has made 14 starts at Fenway, going 5-1 with a 4.60 ERA. His May 19 no-hitter over the Royals was pitched in this building.
Playoff experience: All told in the postseason, Lester is 2-0 with a 1.10 ERA in four appearances, including two starts.
Loves to face: Chone Figgins. The Angels' leadoff man came into this series batting .250 (2-for-8) off Lester. In Game 1, Figgins went 0-for-4 off him.
Hates to face: Gary Matthews. He might have gone 0-for-3 in Game 1, but Matthews is 3-for-6 with two homers, a walk and three RBIs off Lester in the regular season.
Why he'll win: Lester has shown he has the makings of a big-game pitcher, and with the Red Sox looking to avoid a potentially dangerous trip back to the West Coast for a Game 5, this game looks mighty big.
Did you know: According to the Elias Sports Bureau, Lester was the third pitcher to win the clinching game of a World Series in one year and throw a no-hitter the next. Rube Foster (Red Sox, 1915-16) and Sandy Koufax (Dodgers, 1963-64) were the others.