NEW YORK -- Top seed and former champion Serena Williams and four-time champion Pete Sampras of the United States headline play Sunday at the U.S. Open.

Light rain began falling Sunday morning and the start of play was delayed for six hours and 35 minutes before startign around 6 p.m. ET. The weather forecast is for periods of rain throughout the day and into Monday.

Williams, who is seeking her third consecutive Grand Slam title this year, opposes 20th seed Daja Bedanova of the Czech Republic. Williams has defeated Bedanova in both their previous meetings -- the last a 6-2, 6-2 victory in the 2001 Australian Open.

Williams and older sister Venus are seeded one and two at the Open and are attempting to produce the fourth all Williams final in the past five Grand Slam events.

Sampras, seeded 17th this year, will go against No. 33 Greg Rusedski of Britain in men's third round play.

Sampras, who lost in the Open finals the past two years to Marat Safin of Russia and Lleyton Hewitt of Australia, is looking to salvage a dismal year. Sampras is the all-time leader in Grand Slam tournament victories with 13 but has not won a tournament since Wimbledon 2000, a span of 33 events in which he has played.

Sampras owns an 8-1 career mark against the hard-serving left-hander. Sampras won six in a row against Rusedski before losing in three sets in the final at Scottsdale in 2000. Sampras has won their last two meetings in straight sets.

Overall, Sampras has won 20 of his last 21 matches against left-handers. He had a 20-match streak ended when he lost to Wayne Arthurs of Australia in three sets at Cincinnati last month.

Rusedski has an eight-match winning streak but has been forced to play nine sets this week to advance to the third round. Sampras has won both his matches in straight sets.

Three other women's fourth round matches were scheduled for Sunday.

Eighth seed Justine Henin of Belgium faces No. 11 Daniela Hantuchova of Slovakia and Francesca Schiavone of Italy opposes Elena Bovina of Russia in a matchup of unseeded players.

Fourth seed and former champion Lindsay Davenport is scheduled against No.13 Silvia Farina of Italy in a night match.

In other men's third round matches involving highly seeded players, No. 3 Tommy Haas of Germany takes on No. 29 Thomas Enqvist of Sweden, fifth seed Tim Henman of Britain opposes No. 26 Juan Ignacio Chela of Argentina and seventh seed Juan Carlos Ferrero of Spain goes against No. 29 Fernando Gonzalez of Chile.

No. 11 seed Andy Roddick of the United States plays a night match against No. 18 Alex Corretja of Spain.

Also, No. 24 Sjeng Schalken of the Netherland faces unseeded Sargis Sargsian of Armenia, Guillermo Coria of Argentina opposes Arnaud Clement of France and Gustavo Kuerten of Brazil plays Nicolas Massu of Chile.

Henin is 2-0 against Hantuchova, with both victories on hard courts earlier this year. Henin was a semifinalist at Wimbledon and Hantuchova reached the quarterfinals.

Bovina, one of the tallest players on the women's tour at nearly 6-foot-3, has beaten Schiavone in both their previous matches, both on hard courts. They met earlier this year at Los Angeles and Bovina won, 6-3, 6-1.

Davenport is gradually playing her way back into top shape following knee surgery in January that kept her out of action until late July. She is 4-0 lifetime against Farina Elia, losing only one set. The U.S. Open is only the fifth Tour event for Davenport this year and she has made the semifinals of two tournaments and the final of two others.

The 30-year-old Farina Elia had never been past the third round in 10 previous U.S. Open appearances.

Haas is 7-2 lifetime against Enqvist and has won their last six matches. He has been battling tendinitis in both his forearm and shoulder and was stretched to five sets in the opening round by David Sanchez of Spain. Enqvist has not lost a set in advancing to the third round.

Henman and Chela have split their two previous matches, both on clay at Monte Carlo. Henman won in three sets earlier this year and Chela won in three sets in 2000.

Henman, who also had shoulder problems entering the tournament, breezed past two qualifiers in his first two matches and has lost a total of only 15 games in his two victories.

Chela also has won his first two matches in straight sets, including a victory over Michael Llodra of France on his 23rd birthday Friday.

Ferrero and Gonzalez are playing each other for the first time. Ferrero had his best hard court result of the year last month at Cincinnati when he reached the semifinals before losing to countryman and eventual champion Carlos Moya.

Gonzalez has reached the fourth round of a Grand Slam event only once, earlier this year at the Australian Open.

Roddick and Corretja have met only once before and it was in exactly the same scenario. Roddick won in straight sets in the third round of the 2001 U.S. Open, putting Roddick in the fourth round of a Grand Slam event for the first time.