Serena Williams and Maria Sharapova have showed no signs of thawing in their cold relationship as the Australian Open continues, leaving many fans wondering if coach and rumored boyfriend Patrick Mouratoglou will be caught in the middle.

Serena Williams hinted on Thursday that Maria Sharapova had crossed the line in their sometimes-poisonous feud, ABC Sports writes.

Maria Sharapova also refused to take back comments made on a recent article where she confirmed she did not get along with the American tennis star.

Although Serena Williams holds more widely-respected stats than Sharapova, the American tennis star showed frustration throughout the beginning of her first match at the Australian Open.

Despite winning the match, the 32-year-old American tennis star encountered her most glaring error in the sixth game of the second set when a looping backhand from Petkovic landed just over the net to set up an easy winner but Serena Williams was fooled by prodigious backspin and wildly missed the ball with a forehand, EuroSport.com reports.

Serena Williams' coach and rumored boyfriend Patrick Mouratoglou mentioned during a September interview that the American tennis star and Victoria Azarenka are "competing at the highest level," leaving many fans wondering if he predicted a rivalry during the Australian Open.

"Of course they have a good relationship, but it's difficult to have real friends," Mouratoglou said, according to ESPN.

"So, they're not real friends, but they appreciate each other, they're joking; they are friends, but as much as they can be because they're competing at the highest level."

Victoria Azarenka thinks her rivalry with Serena Williams is making her a better player and is looking forward to renewing it over the next four weeks at the Brisbane International and the Australian Open, DNAIndia.com writes.