Serbia's Novak Djokovic celebrates his victory over Germany's Alexander Zverev during their men's singles quarter-final at the China Open in Beijing. (AFP pic)

BEIJING: Novak Djokovic produced a trademark comeback to defeat top seed Alexander Zverev 4-6, 6-4, 6-4 and reach the China Open semi-finals on Sunday, extending his unbeaten record in the tournament.

Playing the ATP 500 event in Beijing for the first time since 2015, the six-time champion was pushed to the limit by reigning French Open and US Open champion Zverev, who delivered 19 aces in the match.

Meeting for the first time in nearly 16 months, Djokovic struggled to contain the German's power in the early stages as the 29-year-old Zverev claimed the opening set, but the Serb gradually worked his way into the match and refused to let his opponent pull away.