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Romania's Halep advanced to the round of 16 where she will battle China's Wang Qiang who defeated 14th seed Kristina Mladenovic, of France, 6-1, 6-2.
The 26-year-old Halep is trying to repeat her success in the California desert in 2015 when she lifted the trophy.
Despite her top ranked status, Halep is still seeking her first career Grand Slam title. She reached her third Grand Slam final earlier this year at the Australian Open where she lost in the final to Caroline Wozniacki in three sets.