Cetkovska edged past Li 7-6 (7-2), 2-6, 6-4 in 2 hours, 46 minutes. Li won two more points -- 121-199 -- over the course of the match but Cetkovska held the advantage in the decisive third set, finishing off three of her four break chances.
It was the second time that the No. 139-ranked Cetkovska beat a world No. 3-ranked player.
Li, however, is already assured of reaching No. 2 in the rankings as of Monday. She is the first Chinese woman to reach that point of the rankings. Peng Shuai Thursday locked up a No. 1 ranking in doubles, as she'll pass Sara Errani and Roberta Vinci for the top spot. No Chinese player has been ranked No. 1 in doubles previously.
Li was the only seeded player to lose in singles Thursday as No. 2-seeded Agnieszka Radwanska was up 6-4, 1-0 when Marina Lucic-Baroni was unable to continue and retired. Third-seeded Petra Kvitova was on the court nearly 2 1/2 hours before taking a 7-6 (7-2), 5-7, 6-2 decision over Lucie Safarova.
Errani, seeded fourth in singles, topped Monica Niculescu 2-6, 7-5, 6-1, also in about 2 1/2 hours, while fifth-seeded Jelena Jankovic beat Alisa Kleybanova 6-1, 6-2 and No. 6 Angelique Kerber topped Klara Zakopalova 6-2, 6-3 in relatively short matches.
Seventh-seeded Simona Halep finished off a 6-4, 6-1 win over Annika Beck by recording eight breaks in eight receiving games.