Top seed Justine Henin will face Maria Sharapova in the quarter-finals of the Australian Open after the pair won fourth-round matches on Sunday.
Henin has not lost a match since the semi-finals of Wimbledon
Henin had been below par in her earlier matches but had no trouble with Su-Wei Hsieh of Taipei, beating the world number 158, 6-2 6-2.
And Sharapova kept up her excellent form with a crushing 6-2 6-0 defeat of fellow Russian Elena Dementieva.
Defending champion Serena Williams later beat Nicole Vaidisova 6-3 6-4.
She will meet third seed Jelena Jankovic after she saw off Australian Casey Dellacqua 7-6 (7-3) 6-1 in an error-strewn match.
Dellacqua, ranked 78 in the world, fought back from 5-2 down in the opener to force a tie-break but Jankovic used her experience to safely negotiate that before dominating the second set.
Nonetheless, the Serbian was far from her best and must improve if she is to seriously threaten the in-form Williams.
"I didn't really play my game," said Jankovic, 22. "It was humid out there and the balls were very heavy, I couldn't even hit my backhand shot.
"Sometimes I feel like Serena's going to blow me off the court. But I have to stay there and play my game and go for the win."
Williams had been expected to face a serious test against Vaidisova and the Czech made the brighter start but failed to convert two break points as the American won the first set.
Vaidisova looked ready to challenge when she broke back for 4-4 in the second but she immediately dropped serve, and Williams wrapped up the win.
"I feel like my serve propels my game and I'm returning well," she said afterwards. "It helps my confidence even more."
Sharapova hit 18 winners and converted six of seven break opportunities as she demolished compatriot Dementieva in 62 minutes.
There are things I'll have to improve and really raise my level in the next matches
"I am really looking forward to my next match against Justine," she said.
"We had a really tough one in Madrid at the end of the year that she just pulled through. She's a great player."
Henin was still not at her best against Hsieh, committing 23 unforced errors, managing just 48% of first serves and being broken when serving for the match, but she was always a class apart.
"Now it's like another tournament is going to start," said the Belgian. "It's gonna be another level.
"There are things I'll have to improve and really raise my level in the next matches."
Ninth seed Daniela Hantuchova and 14th seed Nadia Petrova earlier won rain-delayed third-round matches.
Hantuchova beat Virginia Ruano Pascual 6-2 6-3 to set up a last-16 clash with Russia's Maria Kirilenko.
Petrova had to work a bit harder to see off fellow Russian Ekaterina Makarova 6-1 7-6 (10-8) and will need to improve against Agnieszka Radwanska in round four.
Poland's Marta Domachowska surprised 24th seed Li Na of China 2-6 6-2 6-4, and Caroline Wozniacki of Denmark battled back to defeat Germany's Sabine Lisicki 4-6 6-4 6-3.