Angelique Kerber displaced Serena Williams at the top of the WTA rankings released on Monday.
Kerber had assured her place as world number one by her performances in the Madrid Open last week.
The German, made it to the third round where she faced Eugenie Bouchard and retired with a lower back injury trailing 6-3, 5-0.
1. Angelique Kerber (GER) 7.035 pts (+1)
2. Serena Williams (USA) 6.110 (-1)
3. Karolina Pliskova (CZE) 6.010
4. Simona Halep (ROM) 5.205 (+4)
5. Dominika Cibulkova (SVK) 4.480
6. Johanna Konta (GBR) 4.330
7. Garbine Muguruza (ESP) 4.287 (-3)
8. Svetlana Kuznetsova (RUS) 4.260 (+1)
9. Agnieszka Radwanska (POL) 4.195 (-2)
10. Caroline Wozniacki (DEN) 3.915 (+1)
11. Elina Svitolina (UKR) 3.780 (-1)
12. Venus Williams (USA) 3.752
13. Madison Keys (USA) 3.162
14. Kristina Mladenovic (FRA) 2.965 (+3)
15. Elena Vesnina (RUS) 2.875 (-1)
16. Petra Kvitova (CZE) 2.780 (-1)
17. Anastasia Pavlyuchenkova (RUS) 2.590 (-1)
18. Anastasija Sevastova (LAT) 2.135 (+4)
19. Coco Vandeweghe (USA) 2.082 (+1)
20. Kiki Bertens (NED) 2.064 (-1)