Swansea City claimed a famous FA Cup win as the League One side outplayed Sheffield United on the Premiership team's own Bramall Lane ground.
Two-goal Thomas Butler celebrates with fellow scorer Leon Britton
Thomas Butler was the Blades' tormentor scoring two goals and earning the penalty that Leon Britton converted.
First Butler shot home through a crowd after good work from Bayo Akinfenwa, then coolly struck a left-foot second.
A spot in the fourth round was secured when Derek Geary sent Butler crashing to earth in the United penalty area.
Manager Neil Warnock opted to send out a Blades side showing eight changes and was without suspended captain Chris Morgan and striker Rob Hulse.
But Swansea were also without their suspended top scorer Lee Trundle and injured midfield fulcrum Andy Robinson.
Swansea carved out the better early chances and Rory Fallon should have done better with two efforts.
The striker could have given the League One visitors a gilt-edged start after only two minutes, bursting into the Blades penalty area from the right only to shoot straight at Paul Gerrard.
Fallon had a more difficult chance just after the half-hour mark when the ball fell kindly to him on the edge of the area, but in trying to place his shot allowed a routine save.
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Gerrard had one other alarm to deal with before the break, back-pedalling frantically as Butler's free-kick ballooned off the Blades' defensive wall only to land on the roof of the net.
United finally came alive late in the half, with Alan Quinn and full debutant Kevan Hurst both going close.
Quinn blazed a free header just over the crossbar, then Hurst was denied as Swans stopper Willie Gueret came flying off his line to smother the young midfielder's shot.
United continued in the same vein after the break but Hurst could only graze the outside of Gueret's left-hand post after being teed-up by Christian Nade.
That proved costly as Swansea stunned Bramall Lane with three goals in a 14-minute burst.
Butler was at the centre of United's woe, as the Republic of Ireland midfielder grabbed two quick-fire goals and then earned the penalty that Britton converted for a 3-0 scoreline.
The first came on 53 minutes as Kris O'Leary curled an inviting cross into the United area towards Akinfenwa.
The burly striker's persistence saw the ball break to Butler on the left and he fired through a crowd of defenders to give Swansea the lead.
Still reeling from that blow the Blades found themselves two down, as Britton launched a swift counter-attack that found Butler unmarked on the left once more.
The two-cap man took one touch and then buried the ball under the body of Gerrard.
Incredibly Butler was again not tracked as he burst into the Blades area for a third time.
A despairing lunge from Geary pole-axed Butler and referee Andy D'Urso had no hesitation in awarding a penalty.
Geary had already been booked and was lucky to stay on the pitch, but Britton's calm dink from the spot over the diving Gerrard was reward enough for the Swans.
United put the visitors under severe pressure as they sought a way back into the game, but Quinn was twice denied by first Gueret's agility and then a brave challenge from Izzy Iriekpen.
Sheff Utd: Gerrard, Geary, Bromby, Sommeil, Armstrong, Kazim-Richards, Montgomery, Alan Quinn, Hurst (Law 62), Webber (Tonge 86), Nade (Stephen Quinn 62).
Subs Not Used: Annerson, Lucketti.
Swansea: Gueret, Amankwaah (Iriekpen 43), Austin, Lawrence, Williams, Britton, O'Leary, Tate, Butler, Akinfenwa, Fallon.
Subs Not Used: Oakes, Watt, Jones, Allen.
Goals: Butler 53, 59, Britton 67 pen.
Ref: A D'Urso (Essex).