Justine Henin got away with lapses of concentration at the end of each set to beat unseeded Russian Elena Dementieva 6-4, 6-4 and booked a semi-final place at the Stuttgart Grand Prix on Friday.
Second seed Svetlana Kuznetsova of Russia joined her in the last four of the $650,000 indoor tournament with a commanding 6-3, 6-3 victory over American sixth seed Serena Williams.
Henin goes on to face third-seeded Serb Jelena Jankovic, who came through after defending champion Nadia Petrova was forced to retire through injury in the second set of their match.
The second semi-final will be between Kuznetsova and unseeded Tatiana Golovin of France, after she beat Ukrainian Kateryna Bondarenko 6-3, 6-4 with minimal fuss.
Henin, playing only her second match since winning the US Open on Sept. 8, looked at her untouchable best as she moved 5-0 ahead against Dementieva.
The winner of seven Grand Slam titles was uncharacteristically wasteful, however, and she twice missed chances to serve for the set.
Dementieva was going for her shots, hitting much more powerfully than at the start, but after getting both breaks back the doubts set in again and she double-faulted on set point.
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Henin quickly went a break ahead in the second before again missing the chance to serve out at 5-3. This time she broke immediately to seal victory in 92 minutes.
"I lost a little bit of intensity at the end of each set," said Henin, who will sit out next week's Kremlin Cup in Moscow to let a shoulder problem heal completely. "She's a real fighter. If you give her a bit she'll take it all."
Jankovic only had to play one serious set in her quarter-final.
Petrova had edged it 7-5 on the tie-break before suffering the recurrence of an injury to her left hip, eventually bowing out when 5-1 down in the second.
"I was really surprised she didn't play on, but I know how it feels to play with pain so I wish her a speedy recovery," Jankovic said at a news conference.
"Now I'll go after Henin. I've got nothing to lose."
Like Henin, Williams was playing in her first tournament since the US Open. Defeat will not help her chances of making the season-ending tournament in Madrid.
She managed two convincing wins in the opening two rounds but world number two Kuznetsova simply proved too strong and too consistent, with the American's challenge finally snuffed out when she put a weak backhand wide on the first matchpoint.
"I made so many errors," Williams said. "My balls were just flying everywhere but there was no wind, so I don't know what was going on."
