Arsenal kept the pressure on the two Manchester clubs at the top of the Barclays Premier League as they overwhelmed Birmingham with a 3-0 victory at rainswept St Andrew's.
A Robin van Persie free-kick and Samir Nasri's 13th goal of the season put them in control before an own goal from Roger Johnson added to City's misery.
The Gunners remained in third spot - two points adrift of United and City - after a sixth away success of the season.
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