Paris - Roger Federer officially returned to world No 1 as the latest ATP rankings were released on Monday, replacing old rival Rafael Nadal at the summit.
The 36-year-old, who beat Andre Agassi's record as the oldest-ever No 1 en route to winning the Rotterdam Open title last week, will now look to stretch his lead over Nadal before the start of the clay court season.
"It's unbelievable to be number one again after all these (six) years - this is one of the best weeks of my life," 20-time Grand Slam champion Federer said after beating Grigor Dimitrov in Sunday's final.
Bulgarian Dimitrov's run to the final took him up one place to fourth above Alexander Zverev, while South Africa's Kevin Anderson broke into the top 10 for the first time after winning the New York Open.
Top 20 in the latest ATP Tour rankings:
1. Roger Federer (SUI) 10,105 pts
2. Rafael Nadal (ESP) 9,760
3. Marin Cilic (CRO) 4,960
4. Grigor Dimitrov (BUL) 4,635
5. Alexander Zverev (GER) 4,450
6. Dominic Thiem (AUT) 4,220
7. David Goffin (BEL) 3,280
8. Jack Sock (USA) 2,880
9. Kevin Anderson (RSA) 2,825
10. Juan Martin del Potro (ARG) 2,815
11. Pablo Carreno Busta (ESP) 2,660
12. Sam Querrey (USA) 2,595
13. Stan Wawrinka (SUI) 2,475
14. Novak Djokovic (SRB) 2,470
15. Nick Kyrgios (AUS) 2,395
16. Lucas Pouille (FRA) 2,335
17. Tomas Berdych (CZE) 2,230
18. John Isner (USA) 2,205
19. Albert Ramos-Vinolas (ESP) 1,985
20. Andy Murray (GBR) 1,960