Tommy Smith fired Sunderland into the semi-finals of the FA Cup for the first time in 12 years and ended Sheffield United's aspirations of a second successive appearance in the last four.
Smith, whose two goals dumped Birmingham City out of the competition in the fifth round replay, struck in the 15th minute of a fiercely contested sixth round tie between two sides hell bent on promotion to the Premiership.
Skipper George McCartney linked up down the left with Julio Arca, taking a return pass in his stride to find Smith and a sweetly struck left-foot shot left goalkeeper Paddy Kenny helpless.
"It was a great moment and long may it continue," said Smith. "I'm enjoying things at the moment and this is a fantastic result for the club.
"This has been a fantastic start to the month for me, but three other strikers are fighting for a place and I want to keep my place for the semi-final." Smith had Sunderland's only other effort on target, a fourth minute header from John Oster's centre at the far post producing a fine save from Kenny.
But he was a constant threat to a United defence under severe first-half pressure, only Jason McAteer coming close to increasing the lead.
The Blades had to overcome the loss of striker Ashley Ward after only eight minutes, but apart from a couple of off-target efforts from Peter Ndlovu rarely threatened.
A half-time roasting from manager Neil Warnock, however, and a couple of substitutions transformed the visitors to such an extension the Blacks Cats completely lost their dominance.
Chris Morgan had a close-range header saved, substitute Wayne Allison's shot was charged down and Ndlovu fired over the bar. Sunderland were forced to dig even deeper when Arca was stretchered off injured in the 74th minute.
They held on, however, for a great victory but success in the Cup means another league postponement at Crystal Palace to add to an ever-increasing fixture backlog.
Blades boss Warnock promises his side will be more committed when they return to the Stadium of Light early next month for a crucial promotion clash.
"We showed in the second half we are more than a match for most teams in this division and we will not be bullied or overawed when we return here," he said.
"My missus could have tackled better than some of my players in the first half, when we looked as though we would have been pleased to get off lightly."