Here's a breakdown of how that rest factors in when both pitchers take the mound on Tuesday at 4:30 p.m. ET on TBS.
Jason Hammel, Cubs
Against the Opponent
2015: 3 GS, 1-1, 5.73 ERA
Career: 7 GS, 2-3, 5.97 ERA
Loves to face: Mark Reynolds, .125 (2-for-16)
Hates to face: Jhonny Peralta, .391 (9-for-23), 2 HR's; Jason Heyward, .500, (9-for-18)
Why he'll win: The regular season was one of Hammel's best in 10 years, setting a career high in strikeouts and matching his career high in wins, while posting his second-best WHIP. Hammel has postseason experience, pitching most recently for the Athletics last season. The 33-year old closed the season on a five-inning scoreless outing.
Pitcher beware: After he started the season strong, Hammel struggled with command and the long ball in the second half. He gave up 17 earned runs in the month of September -- the most in any month this season -- while allowing eight walks and four home runs. He also hasn't pitched his best against St. Louis this season, surrendering a combined seven earned runs in 11 innings.
Bottom line: If Hammel can return to early-season form, the Cubs could be advancing in the postseason.
John Lackey, Cardinals
Against the Opponent
2015: 4 GS, 3-0, 0.93 ERA
Career: 7 GS, 4-1, 1.65 ERA
Loves to face: Anthony Rizzo, .083 (1-for-12)
Hates to face: Chris Coghlan, .471 (8-for-17)
Why he'll win: Lackey threw one of his best games against the Cubs in Game 1 of the NLDS, and he benefitted from his experience in the postseason. In 22 playoff appearances, the right-hander now carries a 2.90 ERA with eight wins. Against the Cubs, Lackey has never gone fewer than six innings or allowed more than two runs in an outing.
Pitcher beware: Lackey is going on three days' rest after his longest appearance in more than a month. The Cubs' offense also tallied 14 runs in the past two games, and he could go long at any point on Tuesday with the chance to advance in the postseason.
Bottom line: If there was ever a pitcher to send the Series to a Game 5, Lackey is that pitcher for the Cardinals.