The forward scored twice in ten minutes after half-time as the U’s came from behind to win 3-2 in front of a packed Kassam Stadium.
It sent them into tonight’s fourth round draw, the first time the club have reached that stage of the competition since the 1998-99 season.
Roofe has had an eye for the spotlight since arriving at the club in February and now has 21 goals in his last 36 appearances.
- Michael Appleton confident Oxford United are close to new signing
- Oxford United denied cash boost from Kemar Roofe transfer after Leeds United's failure to make play-offs
- Oxford United young gun Malachi Napa has career immortalised in a comic strip by West Ham
- More details on OxVox stadium bid - but talks 'on hold' due to U's takeover interest
- Liam Sercombe a step closer to Oxford United departure
But this brace against the Premier League side topped the lot for the 23-year-old to become the best moment of his career.
“Yes, 100 per cent,” he said.
“We matched a Premier League side, went a goal down and still managed to score three past them to get a result.
“We’ve got players here who deserve to be playing higher than League Two. We’re showing that each week.
“It was great time to show it in the FA Cup because the game was on TV.”
Roofe was already attracting plenty of transfer speculation, which is set to go into overdrive after his display against top-flight opposition.
But United have been very clear it would take an astronomical bid to prise him away in the January window and Michael Appleton reiterated the stance when asked by a bumper press pack.
The U’s head coach said: “He’s an Oxford United player and he’s happy to be one.
“He doesn’t want to go anywhere because he’s enjoying his football and improving day-by-day.”
Roofe’s goals showed his range of talents.
His first goal was sweetly curled in from outside the box, but the second goal came from a breakaway after a Swans corner – where Roofe won the defensive header.
Watching the replay for the first time while speaking to the Oxford Mail, he said: “I was trying to catch up with play.
“Chris (Maguire) showed great awareness and was unselfish.
“I didn’t have to yell at him, he did the hard work.
“When I shot, it hit the keeper and it was going in slow motion, I thought it was going to go over.
“The first goal I’ve been working on it in training all the time.
“It’s a routine and you just hope it comes off. Thankfully it did today.”
- OXFORD United’s participation in the fourth round means their clash with fellow Sky Bet League Two promotion hopefuls Northampton Town will be postponed.
The game was due to be played at the Kassam Stadium on January 30.