Rafa Benitez explained the decision to introduce Torres in the second half despite the Merseyside derby at the weekend.
The Spain international had an immediate impact and was twice denied by Crewe goalkeeper Steve Collis.
Benitez added: "We brought Torres on to try and score the third goal - every competition is important so we were trying to create more chances.
"So going forward Torres would give us more space and you could see he had two chances to score which if they would have gone in would have sealed the game.
"I was thinking the same with Robbie Keane but we had a problem with Philipp Degen so I was not able to put him on earlier to put him in a position to score."