NEW YORK: Kim Clijsters reached the US Open quarter-finals with a 6-0, 0-6, 6-4 win over No 3 Venus Williams on Sunday to answer any lingering questions about how serious a threat she’d be after a two-year layoff from the women’s tour.

Moving well and and matching every bit of Williams’ power, the former top-ranked Clijsters provided a startling update on the state of her game. It may have also said something about the true state of Williams’ left knee, which she hurt in the opening round, but had refused throughout the tournament to use as an excuse.

After a couple of bagels, both the players regrouped in the third set and played some of the most compelling, solid tennis of the tournament so far. Clijsters grabbed an early break for a 3-1 lead, helped by one of Williams’ five double-faults to close it out, then served out the match, though it was anything but routine.

The Belgian fell behind 0-30 on her serve at 5-4, but just kept banging away. She got it to 30-40, then hit a shot deep into the corner that Williams couldn’t handle. She forced an error at deuce with another deep groundstroke, hit a service winner off the line on the backhand side for the win. This marked the third meeting between Clijsters and Williams at the US Open, and each previous time, the winner has gone on to take the title.

Before her sister lost, Serena Williams cruised through her fourth-round match, winning the final 10 games in a 6-2, 6-0 rout over No 22 Daniela Hantuchova. Serena’s bid for a 12th Grand Slam title will continue with a quarter-final against No 10 Flavia Pennetta of Italy, who saved six match points en route to eliminating No 7 Vera Zvonareva 3-6, 7-6 (6), 6-0.

On the men’s side, No 3 Rafael Nadal overcame a 10-minute medical break for an injury to his stomach muscles to defeat 32nd-seeded Nicolas Almagro,

7-5, 6-4, 6-4. Nadal missed Wimbledon with knee

injuries, and now must deal with injured abs that

first cropped up last month in Cincinnati. His next opponent is No 13 Gael Monfils of France, who advanced when Argentina’s Jose Acasuso quit because of left knee pain while trailing 6-3, 6-4, 1-0.

No 24 Juan Carlos Ferrero of Spain, the French Open champion and US Open runner-up in 2003, moved on when his opponent, No 9 Gilles Simon of France, stopped playing because of a right knee injury, while winners included No 2 Andy Murray of Britain, Argentina’s No 6 Juan Martin del Potro, No 7 Jo-Wilfried Tsonga of France, No 11 Fernando Gonzalez of Chile and 16th-seeded Marin Cilic of Croatia. Murray overwhelmed 195th-ranked Taylor Dent of the United States 6-3, 6-2, 6-2.