Cape Town - Reigning US Open champion Angelique Kerber was handed her first defeat since becoming the new World No 1 after going down in three sets to Petra Kvitova at the Wuhan Open in China.
In a match that lasted nearly three and a half hours, Kvitova finally emerged a 6-7 (10-12), 7-5, 6-4 winner to book her place in the quarter-finals of the Premier 5 WTA event.
The match started in extraordinary fashion, with Kvitova saving five break points during a marathon first game before finally surrendering the sixth.
But Kerber was shaky on serve too, and five more breaks of serve would follow over the course of the next six games, three to Kvitova and two to Kerber, leaving matters all square once again.
It was left to a tie-break to decide the first set, and after narrowly edging it by four mini-breaks to three, Kerber was able to take a one-set lead after nearly 90 minutes on court.
To Kvitova's credit, however, she did not lie down. With Kerber continuing to struggle on serve, she grabbed the second set by three breaks to two and then took a valuable 2-0 lead in the decider after breaking Kerber to love in the first game.
Kvitova had to save no less than seven break points in the eighth game before taking a 5-3 lead, and then found herself in another epic battle in game 10 as she tried to serve out the match.
The Czech squandered five match points and saved two break points before finally clinching an epic victory over the World No 1.
Also exiting the tournament on Wednesday was defending champion and sixth seed Venus Williams, who went down 6-2, 6-2 to ninth seed Svetlana Kuznetsova.
Other to advance to the quarter-finals included Romanian fourth seed Simona Halep, who beat Yaroslava Shvedova 6-3, 6-3, and eighth seed Madison Keys, who edged Daria Kasatkina 6-1, 4-6, 6-4.
Great Britain's Johanna Konta, the 11th seed, also advanced, 7-5, 7-6 (8-6) over seventh seed Carla Suarez Navarro.
In the final match of the day, third seed Agnieszka Radwanska had too much firepower for Caroline Wozniacki, running out a 6-4, 6-2 winner.