The Blades are now a point behind thanks to an early penalty from Barry Robson and second-half strikes from Kevin McDonald and Dave Kitson at Bramall Lane.
Bournemouth, who have also played a game more than United, went down 2-0 at Deepdale to first-half strikes from Preston stars Stuart Beavon and Bailey Wright.
Joining United on 57 points are Yeovil Town, 3-0 winners at home to Scunthorpe United - Byron Webster, James Hayter (penalty) and Paddy Madden on target - and South Yorkshire rivals Doncaster Rovers, who play Crawley on Monday.
Coventry went eighth with a 2-0 victory at Bury's Gigg Lane, Jordan Clarke's early strike supplemented by captain Carl Baker in the second half.
Walsall were held 1-1 at home to Notts County with bottom club Portsmouth scraping the same result at Fratton Park against Carlisle while second-bottom Hartlepool boosted flagging survival hopes with a 2-1 win at home to mid-table Leyton Orient.