United will defend a three-point lead when they take on Chelsea thanks to Wayne Rooney's ruthless finishing.

The striker's clinical couple, one in each half, took his tally to three goals in four days, following his return to the England scoresheet in midweek. But it wasn't all plain sailing for Sir Alex Ferguson's men as they pursued a seventh Premiership win on the spin.

Ferguson's former fledgling Keith Gillespie, playing for his fifth team in the top-flight after spells with United, Newcastle, Leicester and Blackburn, headed home a shock opening goal for Sheffield United in the 13th minute.

Pressure from Colin Kazim-Richards forced Rio Ferdinand to make a hasty clearance from the right-back position and when Blades' left-back Derek Geary whipped in a great cross to the far post, Gillespie sneaked in behind Patrice Evra to beat Edwin van der Sar.

It was the only Sheffield United attack of note in the first half. The Premiership leaders dominated before the goal - Gillespie's former youth team-mate Gary Neville had a shot blocked by Paddy Kenny's legs - and they dominated afterwards. Kenny's best save was reserved for a close-range Rooney header from Neville's driven cross, the keeper diving low to his right to palm the ball round the post when his side were leading 1-0.

For all the home keeper's heroics, the Premiership leaders would doubtless have been in front at half-time had referee Mark Clattenburg not rejected two strong penalty appeals.