Four-time winner Serena Williams survived a major scare before battling into the last 16 at Wimbledon on Saturday, while defending champion Petra Kvitova took the express route into the second week.

Williams was in danger of emulating Rafael Nadal's shock Centre Court exit against Lukas Rosol 48 hours earlier when she lost the first set against Chinese 25th seed Zheng Jie.

That was the first time Serena had dropped a set in the tournament, but the American showed why she is a 13-time Grand Slam champion with a gutsy fightback to finally claim an epic 6-7 (5/7), 6-2, 9-7 win over Zheng, who also lost to Serena in the 2008 Wimbledon semi-finals.

"It was good to win that. I needed a tough match like that and she's always playing me incredibly well," Williams said.

"I'm just fighting everything and playing hard. She plays unbelievable on grass so I just did the best I could."

Serena's reward for her labours is a last 16 clash with history-maker Yaroslava Shevdova.

Kazakh wildcard Shvedova completed the first Golden Set in Grand Slam history as she won all 24 points and conceded none in a 6-0 first set whitewash en route to defeating French Open runner-up Sara Errani.

Shvedova, the world number 65, hit 14 winners and took just 15 minutes to demolish Italian 10th seed Errani in an incredible first set on Court Three.

The 24-year-old, the Wimbledon doubles champion in 2010, couldn't dominate quite so emphatically in the second set.

But she still landed the decisive break to secure a 6-0, 6-4 victory before celebrating with a post-match tweet that read: "Today I laid a golden egg!".

While Serena battled to reach the second week, fourth seed Kvitova barely broke sweat in her ruthless 53-minute 6-1, 6-0 demolition of America's Varvara Lepchenko.

Kvitova has yet to drop a set in defence of the title she won with a shock triumph against Maria Sharapova 12 months ago, and Lepchenko, ranked 53rd, had no answer to the champion's power.

The 22-year-old, who has lost just 13 games in her three matches, blasted 15 winners and forced the out-classed Lepchenko to make 38 errors on Court One.

"When I came here, I wasn't really confident to play on grass, but every round I have played better," said Kvitova, who has watched videos of last year's Wimbledon triumph in a bid to inspire a repeat.

"I watched some videos from last year before the start of Wimbledon. It was so emotional when I saw it. It's nice to know I can do it."

Kvitova will play former French Open champion Francesca Schiavone for a place in the quarter-finals after the 24th seeded Italian, a 2009 quarter-finalist, defeated Klara Zakopalova 6-0, 6-4.

World number two Victoria Azarenka eased through with a 6-3, 6-3 win over Slovak qualifier Jana Cepelova.

Azarenka, who made the semi-finals last year, was never troubled by the world number 178 and will face former world number one Ana Ivanovic in the last 16.

Ivanovic gave the perfect response to her critics as she battled to a 3-6, 6-3, 6-4 win against Germany's Julia Goerges.

The Serbian 14th seed, was once regarded as the female game's brightest young star after winning the 2008 French Open just months after reaching the Australian Open final.

But the 24-year-old has been unable to fulfill her vast potential since then, with some pundits accusing her of lacking the mental strength to succeed at the highest level.

Also through is Austria's Tamira Paszek, the first round conqueror of former number one Caroline Wozniacki.

Paszek enjoyed a 2-6, 7-6 (7/4), 7-5 win over Belgium's Yanina Wickmayer and will face Italian 21st seed Roberta Vinci, who secured a 7-6 (7/4), 7-6 (7/3) over Croatia's Mirjana Lucic.