The problem was the ball hadn’t crossed the line after he had blocked a clearance from home keeper Dillon Phillips.
It summed up the frustration for the 23-year-old striker, who joined Chelsea in the summer following Ipswich Town’s relegation to the Championship in a deal worth £30m.
Delap has failed to convince Blues fans so far, netting just twice in 23 appearances and his last goal coming in a 2-1 defeat at Fulham in early January.
It looked like he had ended that run in the 23rd minute of the tie at the Championship promotion hopefuls, where he had a loan spell in the 2023-24 season.
With the game still goalless, Delap pressured Phillips into a mistake as he tried to clear and the ball looped up, struck the underside of the bar and bounced down onto the goalline.
Yet he showed no urgency to put the rebound into the net.
First Delap raised his arm to celebrate, then appealed to the officials, before collecting the loose ball and having a shot blocked by the recovering Phillips.
Delap, though, recovered impressively from the error to finish the match with three assists as Pedro Neto’s hat-trick and an Estevao Willian strike sent eight-time FA Cup winners Chelsea into round five.
And he was able to joke about the bizarre moment afterwards as he told BBC One: “I swear on my life I almost ran off [the pitch].
“I thought it went in and then I was waiting for the ref to blow his whistle. Obviously, I should have waited for the ref to blow his whistle. It’s silly from me but yeah, crazy.”
Premier League record goalscorer Alan Shearer, speaking on BBC One during commentary of the game, said: “Goodness me. What is Delap doing?
“It is as if he is thinking, ‘I have all the time in the world’. He ambles to it and he takes his time. What are you waiting for?
“Liam Delap has not had a good four minutes. He has given it away twice and missed a sitter. Delap has been poor and he has been given the opportunity tonight. Delap looks very lazy, his performances have to improve.”
