France's Nathalie Dechy held her nerve to beat third seed Anastasia Myskina 6-4 6-2 at the Australian Open.
Myskina committed an embarrassing 45 errors as her game completely fell apart on Rod Laver Arena.
Dechy needed two opportunities to serve out the first set and went a break down in the second but a lacklustre Myskina could not capitalise.
Dechy will face Patty Schynder in a surprise quarter-final after Schnyder's shock win over Elena Dementieva.
It leaves Russia, who had seven players in the fourth round, with only two remaining representatives and Svetlana Kuznetsova and Maria Sharapova face each other in the last eight.
Myskina said her own errors had been solely to blame for her defeat.
"No problems, just a bad day, a bad game. Nathalie played pretty smart against me, that's it," she said.
"I can't say that she won the match. I can say that I lost the match."
But Dechy responded: "I'm in the next round and she's not. I won the match. I played the way I needed to."
Switzerland's Schnyder completed a remarkable turnaround to upset sixth seed Dementieva 6-7 7-6 6-2.
Dementieva looked in control when she took a 4-0 lead in the second set, having edged the first on a tiebreak.
But as the Russian dramatically faltered, Schnyder reeled off five straight games before levelling.
The Swiss player raced through the decider to seal the win in almost three hours.
Dementieva admitted mental frailty had been to blame for her defeat.
"What can I say? I was 4-0, 30-0 up (in the second set). I didn't take my chance," she said.
"There is always a very important game, very important point. If you don't take it, that can change the whole match.
"That's what happened today. She just started to play well. I think I lost my rhythm. I thought it was over already. I don't know how I did it."
Top seed Lindsay Davenport reached the quarter-finals for the eighth time in her career with a 6-2 6-2 win over Karolina Sprem.
The world number one, seeking her first Grand Slam title in five years, raced through the first set and from 2-0 down in the second won six straight games.
"I'm in the quarter-finals and my game's improving. That's a great sign," she said.
The American will face Venus Williams or Alicia Molik in the last eight.