- Serena Williams taken to three sets by Zheng Jie
- Four-time champion will next face Yaroslav Shvedova
- Shvedova took every point in first set in beating Sara Errani
- Defending champion Petra Kvitova eases through
Four-time Wimbledon champion Serena Williams was taken to the brink by China's Zheng Jie before earning a place in the last 16 Saturday.
Williams needed two and a half hours on Centre Court to subdue her 25th seeded opponent, who had reached the semifinals at the All England Club four years ago as a wild card.
On the way she had beaten the American superstar and came close to pulling off another upset after taking the first set tiebreak.
But back came Williams to level before a grueling final set in which Zheng showed her typical determination.
Serving second, she continued to hold until the 15th game when her sixth seeded opponent broke through.
Zheng saved two match points before Williams sealed a clash against Yaroslava Shvedova for a place in the last eight.
"We always have unbelievable matches together and I knew it was going to be tough," Williams told BBC Sport after her win.
Earlier Shvedova had created Wimbledon and WTA history in a remarkable first set against French Open runner up Sara Errani of Italy.
Shvedova took every point, 24 without reply, to break her own record of 23 set in Memphis in 2006.
It was the first time a so-called Golden Set had been achieved in Grand Slam history.
Errani restored some pride in the second set but still slipped to a 6-0 6-4 defeat.
Defending champion Petra Kvitova continued her serene progress into the second week with a 6-1 6-0 romp against Varvara Lepchenko of the United States.
Second seed Victoria Azarenka of the Belarus also had an easy passage, beating Jana Cepelova of Slovakia 6-2 6-3.
And former World No.1 Ana Ivanovic of Serbia showed her improved form as she beat Julia Goerges of Germany 3-6 6-3 6-4.