World number one Simona Halep overcame a sluggish start to beat Wang Qiang 7-5 6-1 at the BNP Paribas Open on Tuesday and book a quarter-final against Petra Martic in the California desert.

The turning point came after a string of unforced errors left Halep trailing 5-4 in the first set, prompting coach Darren Cahill to tell the defensive specialist to work longer points and reduce the error count.

Halep went on to lose only one more game, easily seeing off the challenge of the world number 55 from China.

The 26-year-old Romanian showed no sign of the foot injury that forced her to withdraw from the Qatar Total Open in Doha last month and is well positioned to make a run at reclaiming the Indian Wells title she won in 2015.

• READ: Halep wins, US teen Anisimova's run ends at Indian Wells

First she will have to get past unseeded Croatian Martic, who advanced to the last eight with a 6-3 7-6(4) win against Marketa Vondrousova.

"She is a very tough opponent because she is serving pretty strong and also the forehand has a lot of top spin ... So I will have to work hard," Halep told the Tennis Channel.

Former world number one Karolina Pliskova used her powerful serve to overwhelm 16-year-old Amanda Anisimova and reach the quarter-finals for the third year in a row.

Pliskova's 6-1 7-6(2) win ended a remarkable run for the young American, a wild card who beat ninth seed Petra Kvitova in the third round for the biggest win of her fledgling career.

Pliskova will face 20-year-old Naomi Osaka of Japan, who claimed her 50th career match by defeating Maria Sakkari 6-1 5-7 6-1 to reach her first Indian Wells quarter-final.

(Reporting by Rory Carroll in Los Angeles Editing by David Goodman/Toby Davis/Ken Ferris)

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