Just days after Nick Kyrgios stole headlines around the world for his poor behaviour, Australian tennis star Thanasi Kokkinakis has almost come to blows with American Ryan Harrison in qualifying for the Cincinnati Masters.

Kokkinakis, who was an unwilling member of Kyrgios' sledge to Stan Wawrinka at the Montreal Masters, won the match 7-5, 3-6, 7-6 (7/2) but it was not until after the match that the biggest shots were fired.

During the post-match handshake, American Harrison appeared to pull Kokkinakis in closer to have a heated word although he later said he only told the Australian 19-year-old "good match".

The pair was separated by umpire Mo Lahyani and other match officials and Harrison was heard saying: "These kids have got to get under control".

That prompted Kokkinakis to say he "did nothing to disrespect him" during the heated clash.

Kokkinakis and Harrison traded barbs throughout the match and after one set Kokkinakis told the umpire Harrison had called him a "prick", but Harrison insisted he only called him "kid".

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Then, as Kokkinakis went off for a toilet break, he said Harrison was showing his "true colours" and the world number 124 sarcastically shouted back "Your 'crew' is really cool", presumably referring to Kokkinakis' good friend, Kyrgios.

Later, as Harrison argued a call, Kokkinakis said it was "so draining" playing the 23-year-old and appeared to mock him.

After the match Harrison said he wished he had gone further with Kokkinakis and made it clear Kyrgios was on his mind.

"He's 19. If he wants to get into it, I will bury him," New York Times journalist Ben Rothenberg quoted him as saying.

"Wawrinka should've decked Kyrgios, and I should deck that kid."