That wasn't the plan even several hours prior to the game. Here's what Cardinals manager Mike Matheny had to say in his press conference before the Cardinals took batting practice:
"Yes, we plan on him being available. He was actually going to get a little bit more work today. We ended up kind of holding back on him, making sure he's going to be ready to DH those games [Games 6 and possibly 7 in Boston]. But, yeah, he felt better yesterday, much better than what he thought he was going to feel and even better today. So that's continued to move forward."
At some point during batting practice, though, Matheny and his coaching staff changed their mind on Craig and he's now going to be in the starting lineup and playing first base.
Which is remarkable, because here is how hobbled he was Sunday night in Game 4, limping as he walked to home plate:
Around 3:00 local time (game time is 7:07), Craig was on the field taking groundballs at first base. He didn't look awful, but most grounders were being hit right at him. He didn't really appear to test his lateral movement much.
Still, we know how dangerous Craig can be with the bat. He's coming off an All-Star season and is 4-for-9 this World Series.