As the field at the U.S. Open continues to narrow, top-seeded stars like Venus Williams, Kim Clijsters, and Rafael Nadal are proving their mettle, blocking any attempts at upsets on their way to the finals. Williams, the No. 3 seed competing in her first tournament since recovering from a knee injury, claimed a confident victory over Israel’s Shahar Peer, though she fought hard for it. “It’s always good to have a tough match,” Williams said after the match, which advances her to the quarterfinals. “It was a good challenge.” On other courts, No. 2 seed Clijsters, last year’s singles champ, easily beat 22-year-old Ana Ivanovic. Nadal, the sport’s top-seeded male, will advance to the quarterfinals as well. Meanwhile, Andy Murray, the No. 4 seed among men was ousted by Stanislas Wawrinka of Switzerland.