United boss Neil Warnock had to re-shuffle his side with Dean Windass, on a month’s loan from Middlesbrough, and new £250,000 signing Steve Kabba cup tied.
But it was the Sheffield side that carved out an early chance. Midfielder Peter Ndlovu, with a strong run down the right forced a corner, Michael Tonge picked out Murphy who powered his header wide from eight yards.
The Black Cats escaped again minutes later when Michael Tonge curled in a teasing free-kick. Murphy was the first to react lunging at the ball and stabbing it a foot wide of the target with Jurgen Macho stranded on his line.
Paddy Kenny, a bargain buy from Bury, saved United as Kevin Kyle threaded his way through the United rearguard before finishing with a stinging shot from the edge of the area blocked by the United keeper.
A blunder in the Sunderland defence let in England Under-20 midfielder Tonge who cut inside to find a gap before firing in a right foot shot from 18 yards which was cut out by the ever alert Macho.
The Blades’ hard work paid off in the 54th minute, Phil Jagielka pumping over a swerving cross from the right flank which Varga tried to clear.
But the big defender made a mess of things crashing the ball against the face of the bar and Murphy bundled the ball over the line.
The Sheffield side surged forward again and with Sunderland reeling they grabbed a second goal, carved out by the artistry of Ndlovu.
The 29 year old, still on the transfer list, floated over another peach of a centre and Allison, stretching at the far post, headed the ball over the line from the tightest of angles.