Former tennis player Pat Cash talks with Martin Devlin above about Nick Kyrgios' chances, and whether his 'bad boy' attitude is holding him back. 

Nick Kyrgios needed four hours and 26 minutes to secure a nail-biting victory against Russia's Karen Khachanov in a fifth-set tiebreak.

The Australian sent down 33 aces in what he describes as "one of the best wins of his career".

Kyrgios will face World No. 1 Rafael Nadal in the fourth round, who he has defeated three times in their last seven encounters.

Kyrgios' blunt response to Nadal snub

Nick Kyrgios has followed Rafael Nadal's lead and baulked at an opportunity to speak kindly about his bitter rival following the Aussie's epic five-set thriller against Russian Karen Khachanov.

While Nadal sidestepped having to reveal his true feelings about the Aussie, Kyrgios boldly fielded the same question during his post-match press conference after 1am (AEDT) on Sunday morning at Melbourne Park.

Both players were asked outright if they like each other.

Kyrgios' response has lit the fuse for their fourth round blockbuster, expected to be scheduled for Rod Laver Arena on Monday night.

"I don't really know Rafa," Kyrgios said.

"I've never really hung out with him so I don't really know how he is. I don't really dislike him. I never said I dislike him. I don't know him at all.

"Helluva tennis player. I don't know him as a person. I assume he's OK."

When asked if the pair have ever spoken about their famous Mexico Open falling out last year, Kyrgios expanded further on the mutual respect they have for each other – and the undercurrent of hostility between them.

"At the end of the day we're two different tennis players," he said.

"We go about it completely different. After Wimbledon, I lost. I got beaten by a better player and I shook his hand I looked him in the eye and I said, 'Too good'.

"So regardless, if we don't like each other, whatever, I think there's a layer of respect.

"He's one of the greatest of all time and I also read that he thinks that I'm good for the sport. So there's a layer of respect that we have for each other. That doesn't necessarily mean that we like each other."

The pair have traded verbal barbs ever since Kyrgios' famous win over Nadal in Mexico last year, where the Spanish star said the Aussie "lacks respect for the sport".

Kyrgios responded by labelling Nadal "salty".

Petrol was poured on the simmering rivalry when Kyrgios also mimicked Nadal's service action in his second round win over Gilles Simon.

When asked about Kyrgios' salty dig, Nadal replied: "I really don't care, I am here to play tennis.

"Honestly, I don't care at all. If was funny, good. That's it."

Asked straight up if he likes Kyrgios, Nadal earlier replied: "I don't know. I don't know him personally, honestly, to have a clear opinion.

"It is clear (that) when he does stuff that in my opinion is not good, I don't like (it).

"When he plays good tennis and he shows passion for this game, he is a positive player for our tour, and I want my tour bigger, not smaller.

"So the player who make the tour bigger are important for the tour.

"When he's ready to play his best tennis and play with passion, (he) is one of those guys.

"When he's doing the other stuff, of course I don't like (it)."