Djokovic had breezed through to the last four without dropping a set as he chased a record-equalling sixth title and a first for six years.

But third seed Zverev, who ended the world No.1's hopes of a Golden Slam by beating him at the Olympics in Tokyo, played a superb match to win 7-6 (7-4) 4-6 6-3.

"Every time we play against each other, it's very high level," Zverev said. "This year we played each other five times. ... Every time we played for multiple hours and it was very physical.

"He's the greatest player of all time and I think people forget that sometimes."

On Sunday, the 2018 champion will take on last year's winner, world No.2 Medvedev, who had a straightforward 6-4 6-2 semi-final victory against Norwegian debutant Casper Ruud.

In September at the US Open, Medvedev ended Djokovic's bid for a calendar-year Grand Slam by beating the Serb in the final to lift his first trophy at a major.

Medvedev defeated Zverev in the ATP Final group stages in a match that went right to the wire and will be the favourite having won their last five meetings.

Zverev knows he has the weapons to beat Djokovic and that confidence shone through as he saved a set point at 5-6 in the opener before playing an exceptional tie-break.

Rarely can Djokovic have lost a set where he has played at such a high level, and he seemed rattled in the early stages of the second but responded in trademark fashion to level the match.

A sloppy game early in the third was uncharacteristic, though, and Zverev held firm on his own serve to clinch a fourth career win over the Serbian.

The doubles final will feature Rajeev Ram and Joe Salisbury against Pierre-Hugues Herbert and Nicolas Mahut.

Australian Associated Press