Rooney hails Blues hero Hart
The Manchester United striker was quick to praise City's number one - also his England team-mate - after Hart produced a series of world-class saves in a pulsating 1-1 draw with Borussia Dortmund at the Etihad Stadium.
Rooney wrote on Twitter: "Have to say joe hart has been incredible. For me best keeper in the world."
Although City also created a number of chances, Hart's performance kept them in the contest before Mario Balotelli snatched a first point in Group D with a contentious last-minute penalty.
Hart denied the German champions on eight occasions and Rooney - whose club boss Sir Alex Ferguson was in the crowd - was one of many observers hugely impressed.
Hart could do little to prevent Dortmund taking the lead just after the hour, although he got a hand to Marco Reus' shot, after Jack Rodwell gifted the forward possession.
After that Dortmund stepped up the pressure but were unable to add to their lead and were left seething when Neven Subotic was harshly ruled to have handled at point-blank range from Sergio Aguero.
Despite Hart's brilliance, City have still not kept a clean sheet all season and the defence is a serious area of concern for manager Roberto Mancini.
The Italian said: "We didn't play well. We conceded a lot of chances to them and I am really disappointed by our performance.
"In the first half we had three or four incredible chances, but if you don't defend, if you don't run like Borussia Dortmund did, it is difficult. This is my problem - it is my job. I will solve this problem."
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