Serena Williams fights back to reach last eight at Indian Wells

Serena Williams has not lost since the WTA Finals in Singapore last October

Serena Williams beat Sloane Stephens to reach the quarter-finals of the BNP Paribas Open at Indian Wells, but Maria Sharapova is out.

World number one Williams lost a first set tie-break to her compatriot, but fought back to win 6-7 (7-3) 6-2 6-2.

"I'm still trying to find my bearings," said Williams, 33, who has ended a 14-year boycott of the event. "I have been off a little this week."

Sharapova was beaten 3-6 6-3 6-2 by defending champion Flavia Pennetta.

"Maybe I wasn't playing my best tennis but I was competitive enough," said Sharapova, who made 42 unforced errors and 11 double faults.

"I just wasn't able to step up in the key moments."

The American had refused to play at Indian Wells after being subjected to racial abuse from the crowd in 2001.

She next faces Switzerland's Timea Bacsinszky, who beat Elina Svitolina in three sets.

In other fourth-round matches, Romanian third seed Simona Halep beat Czech Karolina Pliskova 6-4 6-4, and Ukrainian qualifier Lesia Tsurenko upset Canadian sixth seed Eugenie Bouchard 6-7 (5-7) 7-5 6-4.

"I felt heavy out there," said Bouchard. "My legs were sluggish from the beginning of the match.

"I tried to get myself going, but it was kind of a struggle throughout the whole match."

Bouchard served for the match in the second set and was up 4-1 in the third