It was just before 10.30pm when City posted a statement on their website announcing the Italian had been relieved of his duties for failing to achieve this season's "stated targets". The news came on the first anniversary of City's dramatic final-day Premier League title success.
Malaga coach Manuel Pellegrini is the favourite to succeed him, although assistant manager Brian Kidd will take charge for the final two games of the season - against Reading and Norwich - and next week's United States tour.
The statement read: "It is with regret that Manchester City Football Club announces that Roberto Mancini has been relieved of his duties as Manchester City manager.
"This has been a difficult decision for the owner, chairman and board to make and it is the outcome of a planned end-of-season review process that has been brought forward in light of recent speculation and out of respect for Roberto and his extensive contributions to the football club.
"Despite everyone's best efforts, the club has failed to achieve any of its stated targets this year, with the exception of qualification for next season's UEFA Champions League.
"This, combined with an identified need to develop a holistic approach to all aspects of football at the club, has meant that the decision has been taken to find a new manager for the 2013-14 season and beyond."
Mancini's position looked impregnable when he was rewarded for winning the title with a five-year contract last summer.
But City's failure to build on that achievement has cost the 48-year-old, with their title defence being an underwhelming one and their Champions League campaign ending prematurely at the group stage.
They failed to secure the consolation of a second FA Cup win in three seasons as Wigan shocked them in Saturday's final, although it seems Mancini's fate had already been decided before then.