SYDNEY, Jan. 3 (Xinhua) -- Novak Djokovic was knocked out of the Brisbane International in a major quarterfinal upset, while fellow top seed Aryna Sabalenka won through to the semifinals on Friday night.

Djokovic was beaten 7-6 (6), 6-3 by world number 293 Reilly Opelka in one hour and 40 minutes in a late-night match on center court.

The big-serving American hit 16 aces on the way to claiming the biggest victory of his career in his first-ever match against Djokovic.

"The reality is we had nothing to lose coming in against him. He's the greatest player ever so you end up playing more free and you take a lot more risk because it's your only chance. If you play at your normal level, he's going to win every time," Opelka said on court after the match.

The result leaves Djokovic on 99 career singles titles heading into the Australian Open, which he has won a record 10 times.

Earlier on Friday night, world number one Sabalenka beat Marie Bouzkova 6-3, 6-4 in one hour and 44 minutes to set up a semifinal match against teen sensation Mirra Andreeva.

Bouzkova got off to a strong start against the two-time reigning Australian Open champion by breaking serve in the first game of the match but could not capitalize on the early advantage.

In the other women's semifinal, world number 107 Polina Kudermetova will play Anhelina Kalinina.

Opelka will match up against another powerful server, France's Giovanni Mpetshi Perricard, while second seed and reigning champion Grigor Dimitrov will face Jiri Lehecka. ■