Cole was handed his first start in the Premier League for 10 months in Saturday's game and impressed as Chelsea returned to the top of the table with the convincing victory.
Ancelotti was surprised by the quality of Cole's display after such a lengthy lay-off and expects the midfielder to be a key figure in the push for silverware.
"I was impressed with Joe because I know very well how hard he has worked in the last month," said Ancelotti.
Genius"He is a great professional and after 10 months it is not easy for Joe to play like he did. It was a surprise and I am happy for him.
"Joe is a very important player for us. He has fantastic quality in midfield. He is a genius.
"Chelsea played very well and it is not easy to play against us when we put great quality on the pitch. Blackburn did what they could.
"After the defeat against Aston Villa last week we had a good solution about the set-plays. We had a strong defence from set-plays today. We have improved very quick and very well.
"I think it was the best performance since I came here but we have played well in other games.
"I liked this game very much. We played very well and it was a pleasure to see the team play like this.
"We had to pay attention because when you are 1-0 up we know that in football things can happen and it is not a sure result. But at half-time, I asked my team to score more."
Meanwhile, Ancelotti has revealed he will be returning to Italy to be with his sick father Giuseppe.
He added: "It has been a difficult time but this is life. I hope my father will be better in the next day.
"Tomorrow I have a free day and will go back to Italy and return on Monday but I think my father will be better.
"These are difficult days but after Monday I think he will be better and I can stay here without problems."