'That's it': Rafa Nadal responds to Nick Kyrgios' brutal on-court mockery

Rafael Nadal has responded to Nick Kyrgios’ brutal on-court mockery of the World No.1 at the Australian Open.

The duo have long-butted heads and Kyrgios may have stoked the flames of their discontent by mimicking Nadal's serve during his second-round win over French journeyman Gilles Simon.

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Kyrgios was producing some of his best-ever tennis against Simon on Thursday night, but became incensed when he copped a time violation.

The penalty came despite Kyrgios waiting for the crowd to settle before serving.

Feeling his frustration, the crowd booed the umpire after the bizarre call and Kyrgios expressed his disappointment.

But the great entertainer then found time to mock Nadal, impersonating his many ticks by pretending to push his hair behind his ears and pick a wedgie before serving.

"I really don't care," Nadal tersely told a journalist when informed of Kyrgios' impression.

"I am here to play tennis, that’s it. Honestly, I don't care at all. If was funny, good."

Kyrgios explained his actions in his post-match press conference.

"That's part of my motion," he said.

"I started my service motion. There wasn't any extracurricular activities I was doing before my serve to waste time.

"That's the ref's discretion whether I went over the clock or not. It really didn't matter too much."

Kyrgios vows to cut the bulls**t

Kyrgios knew he had to "cut the bulls***" as his on-court antics threatened to derail another Australian Open campaign.

The Australian No.2 was coasting to a routine second-round win over Simon, but as the finish line approached - up 4-2 with the break in the third set - the 23rd seed lost his way.

Two straight double faults from Kyrgios handed Simon a lifeline, with the former world No.6 gratefully accepting to force a fourth set.

In the aftermath, the Aussie directed his fury toward his player's box, which included Davis Cup captain Lleyton Hewitt.

"Of all the things you could say on break point, 'stay tough'," he bellowed.

"That's what I get, every break point, 'stay tough' ... wow. So creative, so creative."

But rather than let the blip become a full-blown meltdown, Kyrgios hit the reset button to bounce back and score a 6-2 6-4 4-6 7-5 victory.

"I just put my head down," Kyrgios said.

"I lost my way a little bit in the third set. I put my head down, I told myself 'just cut the bulls*** and just get to work'.

"I got the break at five-all. It was a good feeling to get through that."

The 24-year-old Canberra native admitted it was the type of match he might have thrown away six or 12 months ago, but stopped short of attributing the turnaround to new-found maturity.

"I was 13 in the world ... I was all right 12 months ago. But, yeah, possibly," he said.

"I did come back from two sets to love down on that court four years ago ... but it could have gone to a dark place and I brought it back and I somehow scraped the win."

Kyrgios joins John Millman and Alexei Popyrin in the last 32 as the only remaining Aussies the men's draw and will next meet 16th seed Karen Khachanov.

He has a fiery history in his only previous clash with the Russian, a three-set loss at the Cincinnati Masters last August in which he was later fined for verballing abusing a chair umpire.

with AAP