BRISBANE: Novak Djokovic was beaten 7-6 (6), 6-3 by big-serving Reilly Opelka in the Brisbane International quarterfinals.

The 37-year-old Djokovic was playing his first tournament of the year. The 24-time Grand Slam champion is preparing for the Australian Open, which starts on Jan. 12 and which he has won 10 times.

“Amazing tennis, Reilly. Absolutely deserved,” Djokovic wrote on Instagram.

Opelka served 16 aces — including one to finish off each set — to earn one of the biggest wins of the American's career.

“I was just focused on my spots,” Opelka said. “If I hit them, it's hard to get them back. If there's anyone that can, it's him.

“We have nothing to lose coming in against him. He's the greatest player ever,” Opelka added. “So you end up playing more free and you take a lot more risk. If you play your normal level or even above a normal level, he's going to win every time. So it's tough in his position because he gets guys that are good players that they roll the dice. And on a on a day like this when a lot of things go my way that's how it works out.”

New coach Andy Murray will join Djokovic in Melbourne.

Opelka achieved a career-high ranking of No. 17 in Feb. 2022 before undergoing hip surgery later that year to remove a benign tumor. He's now No. 293.

“It was tough. A lot of uncertainty, a lot of doubt,” Opelka said.

In the semifinals, Opelka will face Giovanni Mpetshi Perricard, who beat Jakub Mensik 7-5, 7-6 (5). The other semifinal will feature Jiri Lehecka against Grigor Dimitrov.

Lehecka beat Nicolas Jarry 6-4, 6-4 and Dimitrov advanced when Jordan Thompson retired while Dimitrov was ahead 6-1, 2-1.