Serena and Sharapova progress
Serena Williams had few problems reaching the fifth round of the Sony Open but Maria Sharapova battled through.
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The fourth seeded Sharapova was on court for two hours against the 19th-ranked Kirsten Flipkens, losing the first set 6-3 before taking the next two 6-4 6-1.
Consistency has never been a problem for Williams and she swept aside Coco Vandeweghe 6-3 6-1.
Her reward is a meeting with Angelique Kerber - a three-set winner over Ekaterina Makarova - while Sharapova's next opponent had a remarkable day.
Petra Kvitova lost the first set to Ana Ivanovic 6-3 but then rattled off two bagel sets to win 6-0 6-0 in a quite remarkable turnaround that saw Ivanovic double fault 10 times.
Third seed Agnieszka Radwanska was also taken to three sets but came through 7-6 (7/5) 5-7 6-2 against Elina Svitolina.
There were no such concerns for Li Na, with the second seed thrashing 15th seeded Carla Suarez Navarro 6-0 6-2, while Caroline Wozniacki, seeded 11th, hammered Varvara Lepchenko 6-0 6-1.Meanwhile, 10th seed Dominika Cibulkova needed three sets to see off three-time winner Venus Williams, who slipped to a 6-1 5-7 6-3 defeat.