Federer falls to fourth due to Andy Murray's win Sunday in the Shanghai Masters, his third straight ATP title triumph in Asia during the last month.
Murray has few points to defend before the end of the season and with Federer sidelined with an injury, the Scot is well-placed to end the season as world number three for the first time.
Serbia's Novak Djokovic, who has won the Australian and US Opens as well as Wimbledon this year remains comfortably ahead despite taking time off to rest a back injury. French Open winner Rafael Nadal of Spain stays in second.
ATP world top 20-
1. Novak Djokovic (SRB) 13860 pts
2. Rafael Nadal (ESP) 10375
3. Andy Murray (GBR) 7825 (+1)
4. Roger Federer (GBR) 7780 (-1)
5. David Ferrer (ESP) 4710
6. Robin Soderling (SWE) 3500
7. Tomas Berdych (CZE) 3230
8. Mardy Fish (USA) 2965 (+1)
9. Jo-Wilfried Tsonga (FRA) 2880 (-1)
10. Gael Monfils (FRA) 2525
11. Nicolas Almagro (ESP) 2380
12. Gilles Simon (FRA) 2335
13. Andy Roddick (USA) 2120 (+2)
14. Janko Tipsarevic (SRB) 2040 (-1)
15. Juan Martin Del Potro (ARG) 2030 (-1)
16. Viktor Troicki (SRB) 1920
17. Alexandr Dolgopolov Jr. (UKR) 1880 (+1)
18. Richard Gasquet (FRA) 1810 (-1)
19. Stanislas Wawrinka (SUI) 1765
20. Florian Mayer (GER) 1735 (+3)
Murray pushes Federer out of ATP top three
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