Tensions reached boiling point for Roger Federer after the six-time Australian Open winner was reprimanded for allegedly swearing on court.
The 38-year-old was accused by the line judge behind him of uttering a swear word after missing a backhand during his quarter-final match with Tennys Sandgren.
Federer was handed a code violation for an "audible obscenity" by the umpire as a result of the line judge's complaint.
And the bemused Swiss confronted the woman, questioning what she had supposedly heard, before receiving a further warning to leave the matter alone.
Federer was later overheard asking the umpire: "What did I say?
He reportedly later added: "She lives in Switzerland? Give me a break."
It was a rare outburst from Federer, who is often praised for his on-court demeanour, but it was only part of the story unfolding at the Rod Laver Arena.
The 20-time Grand Slam champion had just lost the second set 6-2 to Sandgren and later required the physio for medical treatment.
Sandgren went on to clinch the third set with an ailing Federer struggling to stay in the match, with his hopes of a seventh Australian Open title left in the balance.
