World number one Victoria Azarenka and number two Maria Sharapova crashed out of the Pan Pacific Open tennis tournament in contrasting styles on Thursday.
Azarenka, from Belarus, pulled out citing fatigue, while the French Open champion from Russia went down to Samantha Stosur of Australia 4-6, 6-7 (10/12) in the quarter-finals.
But defending champion and world number three Agnieszka Radwanska of Poland safely went through beating 2010 Tokyo champion Caroline Wozniacki of Denmark 6-4, 6-3.
"Before the tournament on Sunday, I started not feeling very good, just low energy," said Azarenka, 23, giving Angelique Kerber of Germany a free ticket to the semi-finals.
"It took too much energy in the last two matches and today it's not possible for me. Maybe it's because of the tiredness from the whole year. It was difficult to focus between points," added the top seed.
Two-time champion Sharapova took a service break lead first in both sets, losing the advantage both times before coming back from 3-5 down in the second set to force a tie-breaker.
Sharapova staved off four match points in the tie-breaker, but surrendered the match on Stosur's fifth match point.
"Obviously she was up 5-3 and had a chance to win the match comfortably. I had chances in the tie-break (to win the set). Just a one point here, one point there changed a little bit, but it didn't go my way," said Sharapova, 25.
"Although I have a good record against her, she plays long and difficult. She's a steady player on the court, she's a difficult opponent, I could have returned better, but she played a solid match today. She was much more consistent. It's disappointing to lose," added the second seed.
Meanwhile, Stosur said: "It was tough. I knew I lost nine points in a row (at 5-3 in the second set). I just tried to start well in the tie-breaker and I did get off to a good start. I just tried to keep going forward."
"In the tie-breaker, I had match points and she had set points. You don't get a few in a row and you don't know what happens. I just tried to keep going forward," she added.
In the semi-finals on Friday, Stosur will play Nadia Petrova of Russia, who came back from behind to beat sixth seed Sara Errani of Italy 3-6, 7-5, 6-3.