Defending champion Amelie Mauresmo was bundled out of the Australian Open yesterday by an unheralded opponent, but Serena Williams and Roger Federer marched into the quarter-finals.
US sixth seed Andy Roddick also remains in the hunt, digging deep to overcome Mario Ancic in five sets to make the last eight.
Roddick will meet compatriot Mardy Fish, who took care of 16th seeded Spaniard David Ferrer earlier in the day.
But third seed Svetlana Kuznetsova joined Mauresmo on the scrap heap, slumping to Israel's Shahar Peer 6-4, 6-2.
The manner of Mauresmo's 6-4, 6-3 loss to unseeded Lucie Safarova again raised questions of her being a choker.
The second seeded Frenchwoman appeared to have shaken off the tag last year when she won here and then at Wimbledon, but her defense ended meekly against an opponent ranked No. 70 in the world.
"I'm not completely down or whatever, I'm just disappointed," the ousted title holder said.
"But I am going to go back on the court, go back to work, that's obviously what I need," she said.
Safarova, who will now play Czech 10th seed Nicole Vaidisova, who beat seventh seed Elena Dementieva of Russia, said it was the biggest win of her career.
"It's amazing, I still can't believe it, it's incredible," she said.
Peer, 19, was overjoyed at one of the biggest victories of her career over the 2004 US Open champion.
"I have nothing to lose and every match is open," said the 16th seed, who will now play seven-time Grand Slam champion Williams.
Williams rolled back the years to crush eleventh seed Jelena Jankovic 6-3, 6-2, touted as one of the hottest new talents in tennis.
It was the sternest test yet for Williams, a winner here in 2003 and 2005, as she comes back from injury that restricted her to just four tournaments last year.
"It was absolutely sensational, you know I had a lot of fun out there and I just enjoy Rod Laver Arena a lot and I play some of my best tennis here," she said.
"I like being a dangerous floater, it's fun," she said.
Defending champion and top seed Federer wrapped up his 33rd consecutive win against the dangerous Novak Djokovic of Serbia 6-2, 7-5, 6-3, and will next play Tommy Robredo of Spain as he bids for his 10th Grand Slam crown.
"I feel good physically. I've been winning in straight sets every time, plus a day off and I couldn't be better," said the Swiss maestro, who has won in Melbourne twice before and hasn't dropped a set at the tournament.
Roddick ovecame the aggressive net-charging Ancic 6-3, 3-6, 6-1, 5-7, 6-4 in just over three hours with his greater consistency and patience the key to victory.
"Win or lose, I had to turn the tables on his aggression," Roddick said.
"I just put the ball in the court, that helped. He missed a couple of volleys maybe he wouldn't normally miss," he said.
In third-round matches delayed from Saturday by rain, Chinese hope Li Na upset Marat Safin's sister Dinara Safina 6-2, 6-2 to set up an enticing clash with triple champion Martina Hingis.
The ice-cool Li, seeded 19, dominated the game against the Russian ninth seed with a booming serve and powerful forehand to continue a run of form that put her in the semi-final of the Sydney International earlier this month.
Anna Chakvetadze of Russia also made the fourth round, beating unseeded Croat Jelena Kostanic Tosic 6-4, 6-4.
Chakvetadze will play Swiss eighth seed Patty Schnyder for a place in the quarter-finals.
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