Top seed Ivanovic sent crashing by Zheng

(CNN) -- China's Zheng Jie sent top seed and world number one Ana Ivanovic crashing out of Wimbledon in straight sets in an astonishing third round shock on Friday.

The world number 133 won 6-1 6-4 and will face Hungary's Agnes Szavay for a quarterfinals place.

Ivanovic's troubled passage this week finally came to a halt when she became the biggest casualty so far.

French Open champion Ivanovic struggled past Nathalie Dechy in an epic three-set battle on Wednesday and Zheng subjected her to another torrid afternoon.

But this time the Serb could not spring an escape as Wimbledon savored another major upset in a tournament full of surprises.

Zheng appeared to be half the size of her opponent, but looks were deceiving as she produced some ferocious shots from the baseline that belied her stature.

On the few occasions Ivanovic looked her usual self, Zheng struggled to cope, but the tenacity of the Chinese woman ensured Court One belonged to her.

Zheng produced some fearsome strokes from the baseline on her way to storming through the opening set. Ivanovic halted the slump by comfortably winning the opening game of the second set but by the third she was wobbling again.

The net was sproving her nemesis and just to highlight her Achilles heel she blasted another shot low of the target when Zheng was on break point.

Zheng's tenacity then gave her a foothold in a marathon fifth game and when break point arrived Ivanovic nudged the decisive shot wide.

Serving for the match, Zheng overcame a shaky start to fire an unstoppable serve that landed the killer blow.

"The one thing I've learnt about being number one this week is that everyone is so pumped up to beat me," said Ivanovic.

"Now my opponents will always try their best to beat me. In my previous matches here and today, my opponents felt they had nothing to lose.

"They've played some of their best tennis against me. It's something you have to accept and, with time, learn to deal with.

"I didn't play much tennis just before Wimbledon so had only a bit of time to adjust to grass, but I think Zheng played really well," Ivanovic added.

"It was a tough match for me. I'm definitely disappointed with my loss but she's a good player and she plays well on grass. She has very powerful shot. She stays very low, so the balls are coming much faster through the air."

Zheng will now face 15th seed Szavay in the last 16 after the Hungarian battled her way to a 7-6 2-6 6-2 victory over Spain's Anabel Medina Garrigues.

Meanwhile, Serena Williams raced into the last 16 after demolishing France's Amelie Mauresmo 7-6 6-1 in a battle of the former champions.

It was the 10th time in 12 meetings Williams had triumphed over Mauresmo, who was troubled by a thigh injury which required treatment midway through the second set.

Sixth seed Williams plays fellow-American Bethanie Mattek for a quarterfinal place and that side of the draw is now opening up nicely for the two-time champion.

Williams said: "I didn't play my best and was just glad I pulled through. I haven't been playing my best but I'm thinking positive. My volleys are benefiting from my doubles and in the second week I should do better."

It was a match of unforced errors and wildly fluctuating fortunes, which saw four breaks of serve in the first set alone.

Neither woman could assert their authority in that first set, mistakes flowing from their rackets, one surreal smash-volley error from Mauresmo particularly shocking as she contrived to dump the ball in the net from what seemed an impossible position.

Williams' serving was always the more authoritative, however, and she took the tie-break 7-5, courtesy of one brilliant attacking lob winner and several unforced errors from her opponent.

Mauresmo always faced an uphill battle when she lost her serve in the first game of the second set. And her task became tougher when she required a medical time-out to receive treatment after the third game.

Williams coasted into a 5-0 lead before Mauresmo struck back with a string of winners to break serve. It was to no avail as a forehand crosscourt winner from Williams ended proceedings in ruthless fashion.

The unseeded Mattek secured her place in the draw with a straight sets victory over an out-of-sorts Marion Bartoli, last year's runner-up.

Frenchwoman Bartoli, seeded 11, was troubled by a leg injury and failed to produce her best form in a 6-4 6-1 defeat.

The remaining four women's singles matches on Friday all went to form, with a quartet of seeds cruising into the last 16 in straight sets.

Svetlana Kuznetsova celebrated her 23rd birthday with a victory over qualifier Barbora Zahlavova Strycova. The fourth seed overcame two bouts of nerves and a lengthy rain delay to post a 6-2 6-4 win over the Czech qualifier in one hour and 19 minutes.

The Russian will next play 14th-seeded Pole Agnieszka Radwanska, who disposed of Anastasia Pavlyuchenkova of Russia 6-3 6-2.

Eighth seed Anna Chakvetadze came through 6-4 6-3 against fellow-Russian Evgeniya Rodina and will now face Nicole Vaidisova, the 18th seed, in the last 16 after the 19-year-old Czech came past Australia's Casey Dellacqua 6-2 6-4.