James was also on the end of challenges that produced three Brentford yellow cards and a red for defender Ezri Konsa, an incredible individual performance that came little more than two weeks after he almost joined Swansea's Sky Bet Championship rivals Leeds.

Swansea pulled the plug on that deal in the final moments of the transfer window and are keen to tie the 21-year-old flier to a new contract.

James' current contract runs until the end of next season and, asked if Swansea wanted to extend terms, Potter said: "The answer is yes, but it's not as simple as that.

"All parties have to agree. It's a process, you have to make sure everybody's happy."

But asked whether he could move to a Premier League club over a Championship team, Potter replied: "I would say certainly yes – if he was going to move anywhere.

"The ability to sprint repeatedly is at as high a level as you're going to see.

"My responsibility as a head coach is to help him play football, to carry on with his career and to reach his potential because he's still got a lot to do.

"But as you've seen here, he's not playing against bad players. They're not physically weak defenders, but he leaves them for dust."

After Ollie Watkins had rewarded Brentford's first-half superiority, Swansea levelled through an own goal from Bees goalkeeper Luke Daniels before James, Bersant Celina and George Byers put their names on the scoresheet.

Swansea's win took them through to the quarter-finals for only the fifth time in their history, and for the second season running.

"I know we live in this cynical world where it's all about finances," Potter said.

"But we are in the last eight now and the dream to play at Wembley (in the semi-final) at that type of occasion is brilliant for the young players."

Brentford had lost only once in their previous 12 games and were on course for their first quarter-final appearance since 1989.

"We were by far the better side and controlled and dominated the game in the first half," head coach Thomas Frank said.

"But we maybe made the two biggest mistakes and gave it to James.

"He is probably the only player in the country who should not get that ball 30 yards into his own half, kick it 50 yards and then run.

"Then we lost the ball and got the red card. Game over. I've never played a game where we've been so dominant and it goes so wrong."

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