Novak Djokovic has been denied his 100th ATP title after a straight-set quarter final defeat to America's Reilly Opelka.
The 24-time major champion was stunned after being forced to endure big-hitting and long rallies over the course of an hour and 40 minutes.
Taking the first set, Opelka became the first person in the 2025 tournament to deny Djokovic of a set. He struck his 16th ace on match point to claim victory, 7-6 (8-6), 6-3.
The win was arguably one of the biggest of Opelka's career, having previously won seven ATP Tour titles.
Standing at 211cm tall, Opelka once ranked 17th in the world but now sits just inside the top 300.
Novak Djokovic of Serbia and Reilly Opelka of the USA after their quarter-final match. Getty
The 27-year-old American admitted he had considered retirement ahead of his Brisbane International campaign as he had managed just one match in the past two years.
But the "new start" in his career may be all he needed to get back into the swing of the professional circuit.
"[Djokovic] is the greatest tennis player the sport has ever seen. It's difficult being in Novak's position," said Opelka.
"He can scout me or his other opponents all day long. The reality is we have nothing to lose coming in against him.
"You end up playing freer, and take a lot more risks because it's your only chance.
"If you play your normal level, or even above your normal level, he's going to win every time. So, it's tough in his position because he gets guys who are good players who roll the dice, and on a day like this, a lot of things go my way. That's how it works out."
Reilly Opelka of the USA celebrates winning his quarter-final match against Novak Djokovic of Serbia. Getty
Opelka cited the success of American teammates and close friends Tommy Paul, Frances Tiafoe and Taylor Fritz as a leading motivator in his return to the court.
"I watched Novak become the greatest in that two-year period off. You find yourself asking yourself, 'What would Novak be doing in my situation?'," Opelka said.
"Even when you're in a sleeve, you're always trying to kind of maximise, and that's the effect he's had on the sport.
"I stayed the course, even when I was in a cast and on crutches, and was just hoping to have another chance out here like tonight."
Opelka will now shift his focus to France's Giovanni Mpetshi Perricard for the semi finals.