Roger Federer has been fined $3,000 for using an audible obscenity during his Australian Open quarter-final victory over American Tennys Sandgren, tournament organisers said on Wednesday.
The Swiss was handed a code violation for swearing in the third set of Tuesday's match after the lineswoman reported Federer to Serbian chair umpire Marijana Veljovic.
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Federer clarified in his post-match news conference that he had sworn in a "a mix" of languages and said he was frustrated by the way he received the on-court warning.
"Clearly she speaks mixed. Didn't know that. Next time I got to check the (language skills of the) lines-people," the 20-times Grand Slam champion said.
"Honestly, to be frustrated at one point... I think it's normal.
"I found it a bit tough. It's not like I'm known to throw around words and whatever. It's not like the whole stadium heard it either."
Federer went on to save seven match points against Sandgren before winning in five sets to set up a semi-final clash with defending champion Novak Djokovic.
Federer escapes in ‘miracle’ win
Federer feared he was heading home to the Swiss alps before sealing a remarkable 15th Australian Open semi-final berth.
Bidding for his first final four spot and to become the first US man in the Open semi-finals since Andy Roddick in 2009, Sandgren had seven match points in the fourth set.
But the moment got the better of the world No.100 while Federer - playing in his 1512th career match - held his nerve.
"I think I got incredibly lucky today," Federer said.
"I don't deserve this one but I'm standing here and I'm obviously very, very happy.
"I was just hoping that maybe he was not going to smash the winner, you know on that one point, that he would maybe keep the ball in play."
Federer needed a medical time-out in the third set, but didn't believe the injury would hinder his chances of a record-equalling seventh Open crown.
"I've got nothing to do tomorrow and then I play at night so you do feel better in a couple of days and then you just never know again," he said.
"With these lucky escapes, you might play without any expectations anymore because you know you should really be skiing in Switzerland.
"So there you go - I'm lucky to be here and I will make the most of it."