INDIAN WELLS, Calif. -- Struggling with her serve and a rash of errors, Serena Williams overcame a slow start to beat Sloane Stephens 6-7 (3), 6-2, 6-2 in the fourth round at the BNP Paribas Open on Tuesday, extending her winning streak to 14 matches.
Maria Sharapova struggled mightily, too, losing 3-6, 6-3, 6-2 to defending champion Flavia Pennetta, who won her ninth straight match after becoming emotional and leaving the court in the first set.
The Italian went off and cried, saying she "let everything out, screaming, do something."
"For the first two or three games I was OK," Pennetta said. "Then it's coming. Like I never expect. I never do something like that. Normally you go away and you don't want to stay on the court. But for me was important to just keep calm and try to play. In the end I just play really well."
Pennetta had 34 unforced errors and just 15 winners. Sharapova topped her in both categories with 42 unforced errors and 27 winners to go with 11 double faults.
Pennetta broke two-time Indian Wells champion Sharapova twice in the final set, winning the last seven games.
"She got in a really good rhythm," said Sharapova, who didn't notice Pennetta's meltdown. "Everything I gave her she was able to hit back solid with pace."
Williams committed 52 unforced errors and had nine double faults to go with 13 aces and 31 winners in the up-and-down match played in 90-degree (32 Celsius) heat.
"I'm just trying to find my bearings," the world's top-ranked player said. "Little off this week, but like I said, I'm just happy to be here."
Williams set up match point with a 128-mph ace and won when Stephens dumped a backhand into the net, one of her 36 errors.
Williams broke Stephens three times in the final set of her third match at Indian Wells since ending a 14-year personal boycott of the tournament, where she has won two titles.
"The crowd has been really great," Williams said. "It's been really relaxing here. I just feel I don't want to leave."
Stephens recovered after blowing a 3-1 lead in the first set to dominate the tiebreaker that included just one winner, a smash by Williams to trail 3-2.
Williams has been subdued on court, with none of the screaming and exuberant fist-pumping that often marks her matches.
"That's why I was so calm after I lost (the first set), because it was like, I don't really need to win this title," Williams said. "Just being out here is a real win for me and I was just calm through it."
Stephens won four of the final five points and then promptly got broken to start the second set. Her double faults in the first game set up both break points, and Williams cashed in on the second one when Stephens' backhand went long.
"I had some chances and opportunities that I didn't really capitalize on which I should have," Stephens said. "I was playing the No. 1 player in the world. When you don't take your chances, it could be a little tough."
Stephens held to get to 3-2 before Williams won five straight games to close out the second set 6-2 and take a 2-0 lead in the third. They shared a brief conversation at the net during the post-match handshake.
"I have always thought Sloane can be really great," Williams said. "I think she's on the right track. She played really well. It's good to see her doing really well again."
Williams' fans have not been so gracious toward Stephens, who said last week, "Oh, they hate me."
"I understand that they are die-hard fans and I appreciate that. I'm sure she does, too," she said. "But some of the comments and some of the things are so unnecessary."
Stephens said she blocks anyone on Twitter who writes "mean things about someone else."
Jelena Jankovic, the 2010 champion, outlasted 18-year-old Belinda Bencic, 6-3, 3-6, 6-3, to set up a quarterfinal against qualifier Lesia Tsurenko of Ukraine. She beat sixth-seeded Eugenie Bouchard who had 74 unforced errors in losing 6-7 (5), 7-5 6-4.