FA Cup/ Sheffield Utd 0 Swansea City 3:With a relegation battle ahead Sheffield United will be delighted if this remains the low point of their season. But Swansea City, League One play-off hopefuls, swept into the fourth round past Premiership opposition with a swagger that bodes darkly for the defeated.

"We thought we could go on to get four or five and it wasn't luck; it's hardly lucky at 3-0," said Swansea striker Adebayo Akinfenwa.

The home side's performance was such Neil Warnock, usually as protective of his squad as a lioness with her cubs, for once sharpened his claws. He was "humiliated", "let down" and felt certain players should "realise how lucky they are to be in a squad like we've got here and not where they were".

The United manager had made eight changes to the side that lost at Middlesbrough on New Year's Day but refused to offer that as an excuse. "I've no regrets about leaving four or five out because we've had quite a lot of niggles and tiredness, and we had a couple of suspensions, but even so I'm disappointed with a number of players," said Warnock.

"It's no good me mentioning individuals but certain things happened, certainly in the second half, that made me embarrassed to be a supporter . . . It shows what a fantastic job I'm doing - because that is the back-up squad I've got to keep us in the Premier League."

Swansea's Tom Butler, a free transfer from Hartlepool in the summer of last year, swept in the first two goals from the edge of the area and was then chopped down by Derek Geary to give Swansea a penalty that Leon Britton slammed home.

"To go to Bramall Lane and come away with a 3-0 win against Premiership opposition is unbelievable," said Butler. "Games like this can kick-start your season."

How the result will hit United's relegation fight is unsure. Survival in the top flight is the priority but Warnock admitted his attempt to use this game as a confidence-boosting exercise had backfired. His mid-season clear-out continued over the weekend, with Paul Ifill set to join Crystal Palace, but thoughts will now need to be turned to reinforcements. If Saturday's evidence is anything to go by, they will need them.

• Guardian Service