KEY BISCAYNE, Florida (AP):

Top-ranked Serena Williams twice lost five games in a row on Monday, but finished with a flourish and beat China's Zheng Jie 7-5, 5-7, 6-3 to reach the quarter-finals at the Sony Ericsson Open.

Serena Williams, seeking a record sixth Key Biscayne title and her third in a row, smacked an ace with her final swing, then raised a fist and began to pogo. One, two, three, four times she hopped, showing uncommon exuberance over reaching the quarter-finals in a tournament she dominates. But survival is something to celebrate and Williams barely made it out of the fourth round.

"I was just happy to get through it," Williams said, "because at one point I hit a ball into the bottom of the net and I thought, 'wow, I haven't done this since I was a junior.' ... I wasn't playing great."

Also reaching the final eight was number five-seeded Venus Williams, who staged her own narrow escape to beat Agnieszka Radwanska 4-6, 6-1, 6-4. The Williams sisters could renew their sibling rivalry in the semi-finals tomorrow.