Key Biscayne:Previous two champions Kim Clijsters and Svetlana Kuznetsova were ousted in three-setters in the fourth round of the Sony Ericsson Open on Monday.
Clijsters, the 2005 winner, was caught from behind by Li Na of China 4-6, 6-4, 6-2 and defending champ Kuznetsova lost to Shahar Peer of Israel 6-4, 4-6, 6-3.
Former three-time champ Serena Williams set up a showdown with top-seeded Maria Sharapova, who ousted Venus Williams on Sunday, and second-seeded Justine Henin strolled into the quarterfinals by beating Vera Zvonareva of Russia 6-3, 6-2.
In men's play, top-ranked Roger Federer served poorly but still beat Nicolas Almagro of Spain 7-5, 6-3 to reach the fourth round. Federer won his 14th match in a row at Key Biscayne, where he seeks his third consecutive title.
"I'm still kind of looking to come back into the rhythm after not having many matches in the last couple of weeks," Federer said.
He will next face Argentine qualifier Guillermo Canas, who ended Federer's 41-match winning streak two weeks ago at Indian Wells. Canas advanced by beating Richard Gasquet of France 7-6 (3), 6-3.
The final appearance at Key Biscayne for fourth-seeded Clijsters ended with her first ever loss to Li. Clijsters plans to marry and retire this year.
In only her fourth tournament this year, she fell before the quarterfinals for the first time. She was broken in half of her 14 service games by Li, the highest-ranked Chinese player ever, and conceded seven double faults.
Kuznetsova, at a career-high No. 3 ranking, lost the last four games to No. 16 Peer, who repeated her victory from the Australian Open fourth-round.
In a third-round match delayed a day by rain, Serena Williams beat Lucie Safarova of the Czech Republic 6-3, 6-4.
Williams said a heckler bothered her throughout the match, making at least one racist remark before he was ejected.
"The guy said, `Hit the net like any Negro would,'" Williams said. "Every time I missed a shot or a serve, he would say, `That's the way to do it.'"
Tournament officials confirmed Williams was heckled inappropriately, and the man was escorted off the site.
Williams routed Sharapova for her eighth Grand Slam title in January at the Australian Open.
"This is a new day, this is a new match," Williams said. "It's definitely going to be a good match."
Nicole Vaidisova, the youngest player in the top 10 at 17, will be waiting for the winner of the Sharapova-Williams match after defeating Russian qualifier Vera Dushevina 6-2, 6-4.
Henin, who's never given up a set to Zvonareva, stretched her winning run to 11 matches. She will face sixth-seeded Nadia Petrova for her first semifinals berth at Key Biscayne after she overcame Dinara Safina 3-6, 6-2, 6-4 in an all-Russian matchup.
Another Russian, No. 9 Anna Chakvetadze, defeated Mara Santangelo 6-1, 7-5 to set up a quarterfinal with Li.
Agnieszka Radwanska, the 17-year-old Pole who eliminated Martina Hingis on Sunday, lost to Tathiana Garbin of France 6-4, 6-2. Garbin will meet Peer in the last eight.
On the men's side, fourth-seeded Nikolay Davydenko was upset by American qualifier Amer Delic 7-6 (5), 6-3.
Davydenko, who's won three Masters Series titles, lost his first meeting with No. 89 Delic, who hadn't won consecutive matches on the ATP tour until this tournament. Davydenko missed seven of eight break chances.
Jarkko Nieminen of Finland ousted David Nalbandian, a semifinalist last year, 6-4, 7-6 (3). Nieminen won a nine-deuce game at 5-5 to help oust the Argentine.
Also advancing were sixth-seeded Tommy Robredo, seventh-seeded Ivan Ljubicic, Juan Ignacio Chela of Argentina, who needed four match points to put away Tomas Berdych of the Czech Republic, and another Czech, Radek Stepanek.