Torres, who was struggling with a groin injury, scored one of the goals in the 2-0 win at Anfield.
Benitez said: “In the morning, I had decided that he would be involved, but I needed convincing he could start rather than just be a substitute.
“I talked with Fernando on the coach, and that was when I was really convinced that he could play.
“Playing Fernando was a difficult decision. He was not training, the same as Steven Gerrard.
“But after talking with him we decided it was better to start the game with him.”
“You could see he was not 100% fit, but sometimes 80% of Fernando can make a difference,” added the manager.
“We had to be very careful with him, that is why we took him off near the end.
“You have to take care of him. But we were waiting for that final pass and when it came we knew he would score.”
