Thomas Frank is at a loss as to how Brentford crumbled in their FA Cup tie with Swansea City after going into the break with the lead.

Ollie Watkins drew first blood before a Luke Daniels own goal levelled the scores and a breathtaking Daniel James solo run turned the game on its head.

But it was when Ezri Konsa scythed down goalscorer James shortly after the hour, receiving his second booking, which significantly damaged Brentford's chances of regaining a foothold.

After Bersant Celina completed a superb run-and-finish, George Byers burst from midfield to rifle home a fourth goal shortly before time - sending Swansea into the quarter-finals.

Frank said: "We were by far the better side and controlled and dominated the game in the first half.

"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."

Brentford went into the break with a one-goal lead before conceding three goals and going down to 10 men in just over 15 minutes.

Captain Romaine Sawyers' intervention just outside his own box helped engineer a swift counter-attack, which saw Said Benrahma, Neal Maupay and Ollie Watkins all combine for a superb finish.

But the comeback started soon after half time when Celina's set-piece cannoned off the post, came back off Daniels and rolled into the open net.

Four minutes later, it was 2-1 - speedster James was too fast for Kamohelo Mokotjo and burst 60 yards to sweep the ball past Daniels.

Konsa received his marching orders on 61 minutes before Celina beat Sergi Canos and Julian Jeanvier's weak challenges to finish past Daniels.

Then, in added time, Byers arrived late to rifle an effort into the bottom left corner out of Daniels' reach for a fourth.