Dimitrov was leading the Group Pete Sampras match comfortably 6-0, 3-1 when one of the line judges informed the umpire that coach Dani Vallverdu had been trying to convey technical information to his charge.

“He told you to use your forehand so I have to give you a coaching violation,” Nili said.

As it was the first instance of the offence, he was not handed  a point penalty but Dimitrov was nevertheless incensed.

“Who? Him?” the Bulgarian said, pointing towards his box.

“You may not have heard him but [the line judge] did,” Nili added.

However, Dimitrov put the incident behind him and lost just one more game as he secured a convincing 73-minute win over Goffin.

“That was very weird, to be honest. I have no idea why,” Dimitrov said of the incident afterwards.

“But it's fine. It's okay, yeah. I accepted it.

“When you're so zoomed into the match, I don't even pay attention to all that. I think the side umpire went to say that. Okay, I get it.

“But I had a warning from the umpire before that anyway because he says, ‘Next time you get a time violation.’

“Especially when I was on the other side, I guess that rattled him, too.”

Goffin had beaten Rafael Nadal in a three-set match of the highest quality on Monday night, even if the Spaniard’s knee injury hampered him in the decider.

But the Belgian showed none of the venom he had two days previous as it took him the best part of an hour to win a game.

He even briefly threatened to break back in the second set but Dimitrov remained focused and ruthless, breaking Goffin for a fifth time to end the match.

The Bulgarian, playing at the ATP World Tour Finals for the first time in his career, will now face Nadal’s replacement Pablo Carreno Busta on Friday in the knowledge that he is through to the semi-finals whether he wins or loses.