Australian tennis No.1 Nick Kyrgios has taken his latest mid-match controversy into the Twittersphere, getting into a spat with women’s player Donna Vekic about on-court coaching.

Kyrgios appeared to be the beneficiary of court-side coaching from chair umpire Mohamed Lahyani while 3-0 down in his second round US Open match on Thursday.

In a highly unusual move, Lahyani left his chair to beg Kyrgios to start trying against Frenchman Pierre-Hugues Herbert. The move has been labelled a farce by fans and tennis insiders.

“I want to help you. I want to help you,” Lahyani told Kyrgios. “I’ve seen your matches. You’re great for tennis.

“Nick, I know this is not you.”

Kyrgios eventually went on to a 4-6 7-5 6-3 6-0 comeback win. In a statement, the United States Tennis Association said Lahyani was only concerned for the Australian’s health.

But after the match, Croatian world No.41 Vekic – who dates Swiss men’s player Stan Wawrinka – took a shot at Kygrios via Twitter:

Didn’t know umpires were allowed to give pep talks .. 🤔 https://t.co/82k0cQvwZM

— Donna Vekic (@DonnaVekic) August 30, 2018

To which Kygrios fired back: “Ha ha, ironic coming from someone who gets on-court coaching every week of the year and also out of the US Open”.

Kygrios has a history with Vekic. She is the player he named in his infamous “[Thanasi] Kokkinakis banged your girlfriend” mid-match sledge at Wawrinka in Montreal in 2015.

He later deleted his first tweet, replacing it with an apology.

I shouldn’t have tweeted so quickly after the match. Everyone is entitled to an opinion but I can assure you it wasn’t coaching. https://t.co/hvlwPyzC0E

— Nicholas Kyrgios (@NickKyrgios) August 30, 2018

Thursday was a tough day at the office for Kyrgios. He also had to endure a heckler who urged him to “just leave, we want Genie”, referring to Eugenie Bouchard, who was next up on court 17.

“Well, you’ll never have her,” Kyrgios shot back.

Unfortunately for the heckler, Bouchard’s time on court was brief. She went down 6-4 6-3 against Marketa Vondrousova.

Kyrgios’s unusual second round victory has set up a highly anticipated third-round clash with Roger Federer. The winner of 20 grand slams was among those who lined up on Friday to condemn Lahyani’s move.

“That won’t happen,” Federer said, when asked how he’d react if there was to be a similar incident when he plays Kyrgios for a spot in the last 16.

“It will not happen twice in a row. It’s not the umpire’s role to go down from the chair.”

Federer also dismissed the official explanation.

“I am even more upset against the statement of the USTA that is clearly taking us for fools,” he tweeted.

“To err is human but I still wait for explanations. When we players are making mistakes on court we are sanctioned.”

The Swiss star said he didn’t care what Lahyani said to Kyrgios.

“He was there for too long. It’s a conversation. Conversations can change your mindset. It can be a physio, a doctor, an umpire for that matter,” he said.

“That’s why it won’t happen again.”

The umpiring furore has overshadowed what shapes as the match of the US Open’s first week. Federer and Kyrgios have already engaged in three memorable encounters – all decided in third-set tiebreakers.

Their clash is scheduled for Sunday morning (AEST).

-with agencies