Second seed Svetlana Kuznetsova went out of the Australian Open in the third round with a 6-3 6-4 defeat to Poland's Agnieszka Radwanska.
Kuznetsova was well below her best and made 36 unforced errors
Playing under the roof because of rain, former junior Wimbledon champ Radwanska broke Kuznetsova early in the first set and served out the second.
Sixth seed Anna Chakvetadze lost 6-7 (6-7) 6-1 6-2 to Maria Kirilenko.
Eighth seed Venus Williams progressed but had to battle for a 7-6 (7-0) 6-4 win over India's Sania Mirza.
There was no such trouble for fourth seed Ana Ivanovic, who beat Katarina Srebotnik 6-3 6-4.
With rain delaying action on the outside courts, play was only possible under the retractable roofs of the Rod Laver and Vodafone arenas.
Radwanska, who beat Maria Sharapova in the third round of last year's US Open, raced into a 3-0 lead and Kuznetsova soon called for the trainer.
I played against her a few times, always losing, so I said 'no more'
It seemed to do the trick as she quickly levelled but the Russian's inconsistency returned and Radwanska took three straight games to seal the set.
After the pair swapped breaks at the start of the second, Kuznetsova made a dreadful error on a smash to hand Radwanska a break point that she snapped up in game nine.
And despite falling 15-40 down when serving for the match, the Pole remained calm and found some big serves to wrap up the win.
"I played against her a few times, always losing, so I said 'no more'," said Radwanska, who went into the match with a 0-3 record against Kuznetsova.
"It's very exciting, I'm very happy. I tried to make her play left-right, left-right, run her round the court."
Kuznetsova admitted: "This is a pretty tough loss because I think I've been in the best shape ever in Australian Open, and I just didn't make it work.
"I wasn't doing the right things and I lost the match. Playing like this I deserved to lose."
Radwanska, the 29th seed will play Nadia Petrova or Ekaterina Makarova in the last 16.
Williams was stunned by an early break for Mirza, the 31st seed, but broke back and played flawlessly to win the tie-break 7-0.
Games went with serve in the second set until 3-3 when Williams broke and she took her ace count to seven while serving out for victory.
The Wimbledon champion faces Li Na of China or Polish qualifier Marta Domachowska next.
"I felt comfortable throughout the whole match," she said. "Ultimately I had a little more than her and it helped me in the end."
Everything is possible. I've had good wins and my serve is getting better
Ivanovic needed just a single break in both sets to sail into the fourth round and a meeting with either Sabine Lisicki or Caroline Wozniacki.
Despite Srebotnik's best efforts, the fourth seed did not drop her serve and delivered seven aces on her way to sealing victory in 82 minutes.
"I think this was a big step and good win for me," said Ivanovic. "I knew she was a tough opponent and I just had to keep my composure and fight for every point.
"I'm really happy to reach the second week, because that was my goal coming into this tournament.
"But now, everything is possible. I've had good wins and my serve is getting better."
Russians Chakvetadze and Kirilenko played out a tense encounter, with Chakvetadze edging the opening set on a tie-break after neither player managed a break of serve.
But Kirilenko, trying to reach the fourth round of a Grand Slam for the first time, dominated the second set and recovered from dropping serve at the start of the decider.
There were plenty of nerves from the 27th seed as four match points went begging on Chakvetadze's serve in game eight, but Kirilenko converted her fifth chance for a huge win.
"It was a really tough match," said Kirilenko.
"In the first set I was a little bit unlucky and I decided to tell myself 'Maria, come on, keep working, fight for every point' and I did it and I'm so happy."