Messi came off the bench to create Pedroâ€™s equaliser and send Barca into the semis on the away goals rule.
Ancelotti said: "Even if he is not 100 percent fit, he is always a fantastic player.
"We were good in possession and played quickly up the field.
"We didn't just defend like a lot of teams who come here, we caused them problems. But Messi gave his team confidence."