World No1 Novak Djokovic won a bizarre US Open semi-final encounter, 6-3, 6-2, 3-6, 6-2 over 10th-seeded Gael Monfils to enter his 21st career grand slam final Friday night.

Djokovic, who received treatment on his right shoulder multiple times during the match, claimed a 13th consecutive victory over Monfils, who was booed by the crowd for appearing to not try hard enough early on.

The Serb will face the winner of the overnight semi-final between Kei Nishikori and Stan Wawrinka.

In humid conditions both players were far from their best. Monfils swiftly went down 0-5 in the opening set, using bizarre return tactics, before finally getting on the board. It wasn’t until the third set that Monfils started showing glimpses of the form that saw him reach the semi-finals without dropping a set, but the Djokovic regained control to secure victory.