Kemar Roofe scored twice as League Two side Oxford knocked Premier League strugglers Swansea out of the FA Cup.
The hosts recovered from Jefferson Montero's beautiful strike to score either side of half-time.
Liam Sercombe levelled from the penalty spot before Roofe curled into the bottom corner from 20 yards.
And Roofe finished off an attack to make sure Oxford reached the fourth round for the first time in 17 years.
Swansea's fight back, including a second goal from Bafetimbi Gomis, came too late and the home side fully deserved their place in the next round following a strong performance.
The U's are third in League Two and a number of their young players impressed against a Swansea team that gave away the ball too often and looked shaky at the back without their captain Ashley Williams.
"I've got to be delighted beating a Premier League side - but not just that, it's the way we did it," said Oxford manager Michael Appleton.
"I think a few people fancied us beforehand and I did too but we also wanted to play the same way we've been doing it all season and play with no fear.
"We need more days and nights like this at this stadium."