Defending champion Serena Williams ensured there was no repeat result from the 2004 final when she beat Maria Sharapova 7-6, 6-4 in a tense fourth-round contest at Wimbledon on Monday.

The two went toe-to-toe under the blazing sunshine on Centre Court, and Sharapova, the 16th seed, will rue the chances she missed leading 6-4 in the opening set tiebreak.

A quick break of serve at the start of the second gave the American top seed the momentum, and the three-times champion wrapped up the victory when Sharapova sprayed a running backhand wide after an hour and 36 minutes.

Photographs: Reuters

But for anyone wandering past the famous tennis stage, they might have thought two alley cats were at each others throats as a multitude of shrieks, yelps and wails floated out of the arena as two of the hardest hitters went for broke.

"I gave her a run for her money," said Sharapova who fought tooth-and-nail for 96 minutes before going down.

"I thought I played really well and I thought I had my chances. If it was not for her really great serving, I certainly had a real good look at winning the match," said Sharapova.

Six-times champion Roger Federer showed a ruthless streak against one of his best friends on tour when he destroyed Austrian Jurgen Melzer 6-3, 6-2, 6-3 for a place in the quarter-finals.

Melzer, who succeeded Federer as the Wimbledon boys' champion in 1999, recovered from 3-0 down in the opener by breaking the Swiss serve, but it was to be his only success as Federer swept through in an hour and 24 minutes when the Austrian sliced a backhand long.

World number one Rafael Nadal was back at his aggressive best after two five-set matches earlier in the tournament when he crushed unseeded Frenchman Paul-Henri Mathieu 6-4, 6-2, 6-2 in the fourth round.

Nadal, the 2008 champion who could not defend his title last year because of a knee problem, failed to let a drunken fan who had to be led away by police or a back injury to Mathieu distract him from a quickfire win.

After two successive five-set examinations, the 2008 champion was back at his aggressive best to set up an intriguing last-eight date with Robin Soderling.

"Gonna be very difficult match for me I think. Hopefully for Soderling too," grinned Nadal, who came into the news conference chomping his way through one of the 100 bags of Mallorcan biscuits he has at to every tournament.

"He is probably one of the more difficult opponents that you can play on all surfaces today, but especially here," added Nadal about the man he beat 22 days ago in the French Open final.

Taiwan's Lu Yen-hsun sprang the biggest shock of the tournament when he stunned last year's runner-up and fifth seed Andy Roddick 4-6, 7-6, 7-6, 6-7, 9-7 in the fourth round.

Roddick, beaten 12 months ago by Roger Federer following an epic final set 16-14, looked poised for a regulation win when he took the opening set against the world number 82 with a single break in 39 minutes.

But Lu kept his focus and won tiebreaks 7-3 7-4 to put Roddick under pressure and though the American took it to a decider the Taiwanese won through when he fired a forehand winner past the three-times finalist after four hours and 36 minutes.

Lu kissed his fists and raised his arms in triumph after the gripping tussle on Court Two.

"I thought it was a dream, I could not imagine this moment happening," Lu said.

He later said he was dedicating this victory to his father who helped, coached and encouraged him as a boy but who died in 2000 just before he turned professional.

"I'm really upset because my father's already passed away. I make this result. I'm really proud of myself to share this victory with him in the sky. I hope he saw this match.

"So in that moment, I just sit and tell myself, I done it. I did it for my father. I did it for myself also. I did it for all the people who support me," said Lu.

It took a while but the real Kim Clijsters finally showed up on Court One at Wimbledon to topple fellow Belgian Justine Henin 2-6, 6-2, 6-3 in the fourth round.

Neither of the Belgians, whose rivalry goes back almost 20 years, have won the grasscourt grand slam and after a dreadful start, it looked as though Clijsters would be the player left disappointed for another year.

"I was out there somewhere, but I'm not quite sure where," Clijsters, with a white towel draped around her, told a news conference.

"I was just very overwhelmed in the beginning by the speed of her game. She was definitely overpowering me on every aspect of the match, I think. She was serving extremely well, returning extremely well."

Third seed Novak Djokovic shook off a stomach ache and a typical charge from Australian Lleyton Hewitt to win their fourth-round encounter 7-5, 6-4, 3-6, 6-4.

The Serb, who looked to be coasting to victory with a two- set lead, had to call the doctor after complaining he felt sick and needed all his resilience to see off the 2002 champion in two hours and 54 minutes on Court One.

"I was struggling a bit with my stomach. I managed to overcome that," Djokovic said after reaching his fifth straight Grand Slam quarter-final.

"In the third set I was thinking more about that and Lleyton got into a rhythm."