Tensions boiled over as Novak Djokovic defeated Wimbledon champion Andy Murray 7-5 6-3 in controversial fashion to book his semi-final berth at the Miami Masters on Wednesday.

Djokovic, the second seed and three-time champion, was shown on video replay illegally reaching over the net to slam down a Murray return in the final game of the opening set, taking a 15-0 lead.

The outraged Murray wasted much mental effort later arguing with chair umpire Damian Steiner, who made the biggest error by not calling Djokovic out on his violation.

So distraught was Murray after the point that he handed over the set with three consecutive forehand errors.

The Scot later cooled when asked about the incident.

“It was impossible to tell from where I was, but I knew it was close,” he said.

“So that’s why I went and asked Novak, and he told me he was over the net. That was it.

“If it was over the net, it was over the net, and I was right to complain and that’s it. I was correct.”

According to USTA’s website, players are only able to reach over the net when “the spin or wind brings the ball back over the net to the side of the player(s) who hit the shot”.

Djokovic admitted if that was the case, he was wrong to hit the winner and apologised to Murray.

“If I’m not allowed to pass the net, I’m not sure,” said the Serb, who deliberately gave away a point to his opponent in his previous match.

“I thought I was allowed as long as I did not touch. Maybe Andy was right. But it did distract him mentally. After that, he gave the set away.”

Murray rallied briefly in the second set, breaking for 3-2 only to lose the break a game later as Djokovic reeled off four straight games to take the match and book a semi-final against either Roger Federer or Kei Nishikori.