AFP - They last met four years ago and their relationship dates back to almost a decade yet there will be no room for sentiment when Venus Williams faces off with Kim Clijsters in the fourth round of the U.S. Open.

The battle between the two former Flushing Meadows champions has been one of the most eagerly anticipated showdowns expected at this year's tournament and when the duo turned the dream into reality, neither were ready to talk up their chances.

On paper Williams should be the overwhelming favourite to win the contest since she is the world number three while Clijsters does not even own a ranking as she is playing in only her third event after taking a two-year break to start a family.

But the Belgian has already proved to be a thorn on the side of top players such as French Open champion Svetlana Kuznetsova, who was beaten by Clijsters last month, and hence Williams refused to get carried away with her chances.

"She's obviously a very determined woman and very talented. Put those two together and you get great tennis. She's living her dream on and off the court," Williams said after beating Slovakian Magdalena Rybarikova 6-2 7-5 on Friday.

"Obviously, it's great to see her back but I want to advance to the next round.

"Williams leads their head-to-head record 6-4 but Clijsters beat the American en route to winning the 2005 title here and is hungry to enjoy another win at the start of what she calls "a second career."

"It's a big challenge for me. I've got nothing to lose. I'm going to go out there and just give it 200 percent," said the 26-year-old after beating Kirsten Flipkens 6-0 6-2.

"I know what kind of tennis I have to bring. But obviously it's been so long that I stood in front of someone like her, who can play as well as she can.

"I know that serving is going to be very important. I'm going to really have to make sure I get a high first serve percentage in, stay aggressive and keep the unforced errors low."

Some former players have tipped Clijsters to win the encounter as Williams has been struggling with tendinitis in her left nee but the Belgian refused to get distracted by Williams's injury woes.

"She's obviously been playing pretty good, moving ell, so I don't think it's really bothering her that much. She's still playing oubles (so) I assume if it was that bad, she wouldn't be playing both events," said Clijsters.

"I'm going to go out there and ot even worry about the knee. When you play against her, you know that the balls are coming ast. You don't really have time to worry too much about injuries or anything."