ESPN Wimbledon 2008

WIMBLEDON, England -- Venus and Serena Williams have won six of the eight championships contested here at the All England Club this millennium. On Monday, they sailed through to the quarterfinals -- and still, neither has dropped a set.

There has been a Williams sister in seven of those eight finals, and it's looking increasingly likely that there will be another come Sunday. Possibly two.

But while Venus bounded past Alisa Kleynaova 6-3, 6-4, and Serena defeated Bethanie Mattek 6-3, 6-3, the wind in the women's game continued to shift.

New balls -- make that blood -- please. New blood, but not necessarily young blood. On Monday:

• Tamarine Tanasgarn, a 31-year-old qualifier, defeated No. 2 seed Jelena Jankovic 6-3, 6-2.

• Agnieszka Radwanska, 19, of Poland, took out No. 4 seed Svetlana Kuznetsova 6-4, 1-6, 7-5.

• Zheng Jie, ranked No. 133 in the world, the unseeded qualifier who stunned No.1 seed Ana Ivanovic in the third round, sent home No. 15 seed Agnes Szavay 6-3, 6-4.

On a gloriously sunny day when all 16 fourth-round matches on both sides were played, Tanasugarn and Zheng advanced to their first Grand Slam quarterfinals.

As the top seeds have marched through straight-sets victories in recent years, the women's game has been criticized for being too predictable. Now, of course, people will complain that the stars aren't pulling their weight. Perhaps this is the way to view it: Suddenly, the depth among women is startling.

"The reality is that every player is ready to play, especially at these Slams," Venus said. "Everyone comes out with double vengeance, so you just have to be ready. Every match is not a given."

Eight of the top 16 seeds on the women's side departed in Week 1, the most here since 2000 and the highest number in any Grand Slam since the 2004 Australian Open. Thanks for playing our game, Ivanovic and No. 3 Maria Sharapova. For the first time in Grand Slam history, the top two women's seeds did not reach the fourth round.

When Jankovic and Kuznetsova joined Ivanovic and Sharapova on the sidelines, history again was made. The last time the top four women's seeds crashed out before the Wimbledon quarterfinals? Never, going back to 1927, when they started seeding players.

One, two, three, four … No. 5 Elena Dementieva is the highest remaining seed as the women head into Tuesday's quarterfinals.

The men's favorites are taking a beating, too.

Ten of the top 16 seeds failed to survive and advance to the second week, including a straight flush (as it were) of No. 3 Novak Djokovic, No. 4 Nikolay Davydenko, No. 5 David Ferrer, No. 6 Andy Roddick and No. 7 David Nalbandian.

Thus, three of the four 2008 Grand Slam champions (Djokovic, Sharapova and Ivanovic) lost before the fourth round.

The women's game in particular finds itself open to suggestion. Since Roger Federer became the world's No. 1-ranked player in February 2004, there have been six different No. 1 players on the women's side and 14 total changes at the top. There could have been a seventh No. 1, but the defeats of Jankovic and Kuznetsova mean Ivanovic will remain (barely) on the top of this wobbly pile.

"Strange times in women's tennis," mused Pam Shriver, an ESPN analyst. "When No. 1 and No. 3 lost in the third and second rounds, respectively, to players outside the top 100, well, that may not happen again for a long, long time.

"It's a convergence of a lot of things. Who knew Sharapova's serve would go off so badly? Or that Ivanovic would be mentally tired?"

Grass, according to Shriver, contributes to this instability. Since the season is so short -- a single month -- it is the surface most difficult to assimilate to.

"The Williams sisters play well on that surface," Shriver said, "but most of the other women seem uncomfortable on it.

"Things crater quicker on grass more than any other surface. Things happen really fast."

That is precisely what happened to Jankovic, who was slowed by what she described as a meniscus tear in her left knee.

"I was very, very late on every shot," she said. "I was always one step behind, away from the ball, so it was very hard for me to follow the game."

Tanasugarn previously was 0-for-8 in fourth-round Grand Slam matches. She fell to her knees and cried immediately after the victory and now has won an unlikely 11 consecutive matches, including her victory last week at Hertogenbosch, where she beat French Open finalist Dinara Safina in the final, and a clean run through qualifying.

"Can I say, 'Wow, wow, wow'?" Tanasugarn said. "It was very great feelings because I'm in the fourth round so many years, and I make [quarterfinals] this year."

Tanasugarn was born in Los Angeles and has dual citizenship in Thailand and the United States; she carried Thailand's flag in the 1996 Summer Olympics in Atlanta. Her previous Wimbledon highlight came in 1995, when she beat Anna Kournikova in the semifinals of the junior tournament.

The bad news? Tanasugarn is 0-for-6 -- 0-for-12 in sets -- against Venus.

"I play her many times, and she kick my butt," Tanasugarn said. "For me, I'm just happy to be in quarterfinals. No pressure at all for me."

Radwanska is in a different class. Still a teenager, she reached her first Grand Slam quarterfinal back in January in Australia and now has made the elite eight of a major two times in three. She trailed Kuznetsova 4-1 in the third set, then rallied to win.

Serena won the only match she and Radwanska have played earlier this spring in Hamburg. Radwanska, however, has become a tough out. She has won 40 of 51 matches this year, the most of any remaining woman, and might have a scouting advantage in this quarterfinal match.

She watched some of Serena's second-round match -- a 6-4, 6-4 victory over her younger sister Urszula. Given the state of the women's game, Serena will not be caught looking ahead to meeting her sister in the final.

"There's a lot of depth in women's tennis," Serena said. "Everybody, I've been saying for awhile, is playing so well. You can't underestimate anyone, no matter who you're playing, whether it's the first round or the final.

"You have to play everyone with the same tenacity."

Greg Garber is a senior writer for ESPN.com.