WIMBLEDON, England (AP):

Rafael Nadal has helped his nation cure its longtime aversion to lawn tennis and he'll be one of three Spanish men playing today in the fourth round at Wimbledon.

Switzerland, France, Russia and Croatia have two players apiece among the final 16.

Britain - which last won the men's singles title in 1936 - advanced one man to the second week, as did Australia, Germany, Serbia and even the island of Cyprus. And the United States? None.

The nation that produced Andre Agassi, Don Budge, Jimmy Connors, John McEnroe, Pete Sampras and Bill Tilden finds itself in a collective slump. And there's no sign of a turnaround.

"We've been struggling for a long time and it has just gotten worse," said Gene Mayer, a former top-five player who coaches privately in New York. "We just are producing no players."

So far Wimbledon has been jolted by a series of first-week upsets that decimated the seeding lists. Six of the top-10 seeded men were knocked out before the fourth round: No. 3 Novak Djokovic, No. 4 Nikolay Davydenko, No. 5 David Ferrer, No. 6 Andy Roddick, No. 7 David Nalbandian and No. 9 James Blake.

Top seeds falling

Among the women, two of the top three-seeded players are out - No. 1 Ana Ivanovic and No. 3 Maria Sharapova.

For the first time since 1926, only one U.S. male - No. 102-ranked Bobby Reynolds - reached the third round at Wimbledon. He lost Friday.

The drought is less noticeable on the women's side only because of the Williams sisters, who have combined for 14 major titles. They and Bethanie Mattek were the lone Americans to survive the first week at Wimbledon.

Venus and Serena Williams will play their fourth-round matches back-to-back today on Court 2 - nicknamed the 'Graveyard of Champions' for its history of upsets of Wimbledon winners. Not only that, the sisters are scheduled to play doubles on the same court the same day.

Between them, the sisters have won six of the last eight women's Wimbledon singles titles. Defending champion Venus is a four-time winner and Serena is a two-time champ. They are in opposite halves of the draw and could meet in the final next weekend.

Venus takes on teenager

Venus will be up first today against 18-year-old Russian Alisa Kleybanova, with Serena following against Mattek. Later, they will team up in doubles against Anabel Medina Garrigues and Virginia Ruano Pascual.

Eight American men lost in the first round, including Olympians Sam Querrey and Robby Ginepri. Roddick and Blake lost in the second round.

This second Monday of Wimbledon is the busiest of the tournament with all fourth-round men's and women's matches on the schedule - 16 in total. Three matches each are scheduled on Centre Court and Court 1.

Roger Federer's next opponent today is the last man to win the title before the Swiss star began his run of five straight championships - Lleyton Hewitt, the scrappy Australian who won the title in 2002. The two have met 20 times - with Federer winning the last 11 dating back to the 2004 Australian Open and holding an overall edge of 13-7. In their only two previous Wimbledon match-ups, Federer won in the 2004 quarter-finals and 2005 semi-finals.

If Federer gets past Hewitt, he could face a dangerous floater in the quarters. Mario Ancic was the last player to have beaten Federer at Wimbledon - he did so as a qualifier in the first round in 2002.

Nadal faces 17th-seeded Mikhail Youzhny of Russia.