In what are expected to be largely dry conditions on Monday, men's top seeds Roger Federer and Andy Roddick will have to defuse the dynamite serves of Croatian Ivo Karlovic and German Alexander Popp respectively.

Two other clashes stand out -- 2002 champion Lleyton Hewitt's meeting with Spain's Carlos Moya and Briton Tim Henman's showdown with Australian Mark Philippoussis, who was runner-up to Federer last year.

"I've never faced somebody so tall," said Federer of 6ft 10ins (2.08m) Karlovic, who caused a sensation last year by eliminating defending champion Hewitt in the first round.

"Everybody is talking about that big serve. I would like to face it and see how I can kind of play with it. We'll see how big it is."

Roddick, beaten in the semi-finals by Federer last year, is no slouch in the serving department either, boasting the world's fastest delivery of 153 mph. He will face a similar challenge to Federer against Popp but the confident American is, as ever, up for it.

"Once you make the second week, you start feeling like you're in the trenches," he said. "That's where I feel like I am right now."

Spain's Moya has never previously been beyond round two at Wimbledon and will have his plate full against Australian Hewitt, who is showing signs of recapturing the form that made him world number one not so long ago.

As on People's Sunday, the man the home fans will have come to see is Henman.

His match against Philippoussis is a rematch of their 2000 fourth-round encounter which the Australian won in five scintillating sets.

The fifth-seeded Briton, trying to end a 68-year wait for a home men's champion, has been in better form than Philippoussis overall this year but he too will have to neutralise a punishing serve to advance.

"I know the way he is going to play," Henman said. "He serves big and sometimes there isn't too much you can do. He is going to be coming at me with his first and second serves and that suits me fine."

SERENE SERENA?

In the women's fourth round defending champion Serena Williams believes she is on a roll.

"I'm getting better each round. This year I'm feeling better because I've been through a lot physically," said the 22-year-old, who only returned in March from knee surgery.

Americans Jennifer Capriati and Lindsay Davenport, seeded seven and five respectively, face intriguing battles with younger Russian opponents.

Tenth seed Nadia Petrova faces Capriati, probably for the right to play Serena in the quarters, and 12th seed Vera Zvonareva tackles 1999 champion Davenport.

Petrova upset Capriati in three sets in the 2003 French Open fourth round with some fine net play and the American said: "I think she'll be trying a lot of that so it's important for me not to let her."

Russian upstart Maria Sharapova has, in theory, an easier task against American Amy Frazier. The Siberia-born 17-year-old, though, will be mindful that Frazier ousted Russian French Open champion Anastasia Myskina in round three.

Dangerous Croatian Karolina Sprem, who inflicted the only major shock of the first week by beating twice former champion Venus Williams in the second round, plays Bulgaria's Magdalena Maleeva for a place in her first grand slam quarter-final.