Top seed Jelena Jankovic was bundled out of the Pan Pacific Open in a 2-6, 7-5, 7-5 defeat by Russian Svetlana Kuznetsova in Friday's quarter-finals.
The loss ended the Serb's hopes of recapturing the world number one ranking from Serena Williams this week following her recent loss to the American in US Open final.
Olympic champion Elena Dementieva became the sixth of the tournament's top eight seeds to bow out of the Tokyo event as the Russian was upset 6-3, 6-4 by Slovenia's Katarina Srebotnik.
Jankovic tore through the first set but, after being pegged back by Kuznetsova, both players struggled for consistency in the decider, which contained eight breaks of serve.
A double fault gave Kuznetsova a 6-5 lead and the Russian's nerve held as she closed out proceedings with a kicking serve and a sharp backhand drop volley after almost two-and-a-half hours.
"I knew I had to take risks in the third set," the former US Open champion told reporters after beating Jankovic for the fourth time in six meetings.
"She made a few double-faults on important points. I guess she was scared because I was attacking.
"In Russia we say if you don't take risks you don't drink champagne."
Jankovic, who had fumed at the chair umpire and yelled at herself as her game began to unravel, was still in a black mood an hour after the match.
"I'm frustrated," she said. "I was unlucky on a couple of big points. It just wasn't my day. I have to learn from this."
Kuznetsova will face Srebotnik in Saturday's semi-finals.
Fourth seed Dinara Safina briefly flirted with disaster before advancing with a 6-4, 6-7, 6-2 win over Estonian qualifier Kaia Kanepi in the day's last quarter-final.
Meanwhile, Nadia Petrova sprung her second surprise in 24 hours by beating sixth seed Agnieszka Radwanska of Poland 6-3, 6-0 in the bottom half of the draw.
The Russian, who stunned Serb Ana Ivanovic, the second seed in Tokyo, in Thursday's second round, takes on compatriot Safina in the semi-finals.