You never quite know what you are going to get with Nick Kyrgios and the controversial Australian broke new boundaries here on Thursday at the US Open when he beat France’s Pierre-Hugues Herbert 4-6, 7-6, 6-3, 6-0 after appearing to receive a pep talk from the umpire.

Kyrgios was a set and 3-0 down in the second-round match and showing an apparent lack of effort when Mohamed Lahyani, the umpire, got out of his chair at a changeover to talk to him. Lahyani, who is Swedish, appeared to encourage the world No 30 to pick up his game and seemed to tell him: “I want to help you. I know this is not you.”

Considering that players are not allowed to receive on-court coaching, the umpire’s behaviour was immediately called into question. However, the tournament referee gave no indication that any action would be taken against the umpire and said in a statement that Lahyani had simply been concerned that Kyrgios might need medical attention.

Herbert nevertheless said it should not have been Lahyani’s job to do what he did and thought the tournament should “maybe give me the prize money of the winner”.

After Lahyani’s words of encouragement Kyrgios’ performance improved markedly. The Australian went on to level the second set at 5-5 and then won the tie-break 8-6. Kyrgios eased through the next two sets for the loss of only three games and eventually completed his victory after two hours and 47 minutes. He now plays Roger Federer, who beat Benoit Paire 7-5, 6-4, 6-4.

“He was just concerned about how I was playing,” Kyrgios said afterwards when he was asked about Lahyani’s intervention. “He was like: ‘Nick, are you OK?’ I was like: ‘Yeah, everything’s actually fine.’ I just wasn’t feeling great.”

Nick Kyrgios was in a typically feisty mood (AP)

Kyrgios denied that Lahyani had encouraged him. “He said he liked me,” Kyrgios said. “I'm not sure if that was encouragement. He just said that it's not a good look.

“Look. I wasn't feeling good. I know what I was doing out there wasn't good. I wasn't really listening to him, but I knew it wasn't a good look. It didn't help me at all. I was down 5-2. If it was 3-0, and maybe if I would have come back and won six games in a row, fair enough. But it didn't help me at all.”

Kyrgios said there had been past incidents, in Shanghai and Cincinnati, when umpires had spoken to him in similar fashion. “InCincinnati two weeks ago against [Juan Martin] del Potro, the exact same thing happened. I wasn't putting forth my best performance.I did the same today. The umpire was like: ‘Nick, you can't be doing this. It's a bad look.’ The same thing happened there.”

Kyrgios needed firing up to overcome Pierre-Hugues Herbert (USA Today Sports) (USA TODAY Sports)

Asked how he had felt when some of the crowd booed when he was playing badly earlier in the match, Kyrgios said: “I love it. When I was up 40-0 at the end, I put my ear to the crowd. I just wanted to hear them boo again.”

Herbert, who said that Kyrgios played much better after the incident, thought Lahyani had been in the wrong. “The umpire doesn't have to talk to him at all,” he said. “The only thing he can tell him is: ‘Yeah, pay attention, because if you continue like this, I'm going to give you a warning.’ Something like this.

“He can tell him from the chair. He doesn't need to go down. He doesn't need to say the words he said. I think this was not his job. I don't think he's a coach, he's an umpire, and he should stay on his chair for that.

“I don't think he has to go down and take the position of a coach, like you see on the WTA tour. I don't know yet if it would have changed anything. I just know he doesn't have to do that.

“I think Mohamed is actually a really good umpire. I think he knows everybody. I think he cares for Nick. He cares for the show also, because people were going after the first set. Everybody was there for the start. When they saw Nick in a bad mood, I would say, for the first two sets, they started going away.

“Like everybody, I think Nick today could be an amazing player. Just sometimes he's mentally not here. I don't know where he was for the first two sets. I know he was on court after when he started playing, when he kicked my ass and was much better than me.”