Danielle Collins accused the chair umpire of bias towards Ash Barty in an ugly outburst at the Adelaide International on Wednesday night.
Barty suffered another baffling collapse to lose 6-3 6-4 to Collins, blowing leads in both sets to crash out of the tournament where she was the defending champion.
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Just seven days after losing in the Australian Open quarter-finals, Barty suffered a similar capitulation to crash out in Adelaide.
Collins scored the biggest win of her carer and first over a World No.1, however her victory was somewhat overshadowed by an argument with the chair umpire in the opening game.
The American was left fuming when the chair umpire wouldn't let her challenge a line call because she hadn't stopped play immediately.
Collins waited until she saw that her own ball had gone out before asking the umpire to check on Barty's preceding shot.
"The ball was a foot out," Collins told umpire Tom Sweeney.
"Don't give me that. I hit three aces inside the singles line and then I didn't get the point and the other girl did.
"Please challenge the call. The ball was a foot out."
Sweeney replied: "You were waiting for this one, and then you wanted to come back to this one."
To which Collins shot back: "Oh really? You think I'm strategically doing that when the ball is far out?"
After losing the game, Collins then made the explosive claim that Sweeney was favouring Barty because she's Australian.
"That's the most ridiculous thing I've ever seen in my entire life," she said.
"The ball was this far out. I'm sorry, it's unacceptable.
"I immediately, after I hit the ball - said? What difference does it make? I'm waiting for a call. Sometimes the calls aren't until a second after."
"You're doing it because she's Australian."
Sweeney then warned Collins, saying: "Danielle, please be careful in that sort of questioning."
Fans took to social media to slam Collins' actions.
Barty disappointed by second collapse in a week
Barty says she was simply outplayed by Collins, as the Australian top seed's title defence crashed at the first hurdle.
Barty took a wildcard entry to defend her Adelaide crown after her Australian Open loss last Wednesday to Karolina Muchova.
But the Queenslander, after being gifted a first-round bye, fell flat after promising starts to both sets against world No.37 Collins.
In the first set, Barty skipped to a 3-1 advantage but lost the following five games.
And the second followed a near-identical theme: Barty led 4-1 before Collins took the next five games.
"It's disappointing to have two sets in a row where I went on a run of losing games," Barty said.
"But also in that second set, I felt I got away from what was working on serve and just gave her an opportunity to get back in the match."
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