Over the years City have been mocked by United fans and this was their chance for payback.
As the United players drowned their sorrows two miles away at the club's annual player of the year awards night at Old Trafford, City players and fans partied on the streets.
Manager Mancini wore a blue and white City scarf as he waved to supporters, many with their faces painted in the club's colours, from the steps of Manchester town hall.
"I love our supporters they are incredible and I really love days like this," Mancini said.
"I hope we have many more. I didn't sleep much at all last night because it was impossible with the emotions of what happened on Sunday. But I am very happy. I need a rest now - we all do - so we can come back fresh for the start of next season."
Image: Manchester City players including their captain Vincent Kompany, centre, celebrate with the trophy in the city centre before a bus parade the day after their team won the English Premier League, Manchester, England, Monday May 14, 2012.