The top 20 in the ATP world rankings were unchanged Monday heading into the US Open, with Novak Djokovic topping the list.

Britain's Andy Murray remained second with Stan Wawrinka ahead of fellow Swiss Roger Federer in third.

ATP Top 20:

1. Novak Djokovic (SRB)            14,840 pts
2. Andy Murray (GBR)                9,305
3. Stan Wawrinka (SUI)              4,980 
4. Roger Federer (SUI)              4,945 
5. Rafael Nadal (ESP)               4,850 
6. Milos Raonic (CAN)               4,805
7. Kei Nishikori (JPN)              4,165
8. Tomas Berdych (CZE)              3,570
9. Marin Cilic (CRO)                3,515 
10. Dominic Thiem (AUT)             3,205