Sir Alex's team selection was the first big surprise of the night, with his decision to make four changes to the side that drew 4-4 against Everton eight days earlier raising plenty of eyebrows.
In came Chris Smalling and Phil Jones (for the injured Jonny Evans and Rafael), while Ji-sung Park was handed his first league start since January and deployed in the centre of midfield alongside Michael Carrick and Paul Scholes. Ryan Giggs started on the left flank, while Nani was given the nod ahead of Antonio Valencia on the right.
The Reds' 4-5-1 formation – with Wayne Rooney as a lone striker – hinted at a cautious, containing approach from the visitors and yet it was United who asked the first questions as Patrice Evra won a corner within a minute and Carrick's hooked effort was blocked on the way to goal.
United continued to enjoy the lion's share of possession in the opening exchanges but the attacking limitations of the Reds' formation became obvious when Rooney, released by a lovely through-ball from Carrick, was forced to hold the ball up instead of delivering a cross into a penalty area devoid of red shirts.
City soon gained a foothold in the game, although it took until the 16th minute for the Blues to work their way in behind United's defence. And when Samir Nasri did thread a pass through to Carlos Tevez, the Argentine's low cross was well cut out by Jones.