Top seed Ana Ivanovic has been forced to withdraw from the Qatar Open in Doha with an ankle injury, one of three seeds to exit at the third-round stage.
Ivanovic hopes to be fit to play in Dubai next week
Poland's Agnieszka Radwanska was handed a walk-over into the quarter-finals after Ivanovic pulled out.
Wimbledon champion Venus Williams lost 6-3 6-3 to Dominika Cibulkova, while second seed Svetlana Kuznetsova lost 6-3 7-6 (10-8) to Sybille Bammer.
But third seed Jelena Jankovic and fourth seed Maria Sharapova progressed.
Jankovic beat Ai Sugiyama of Japan 6-1 6-2, while Sharapova saw off Thailand's Tamarine Tanasugarn 6-2 6-2.
When I was little she was one of my idols, so I still can't believe it
Dominika Cibulkova on beating Venus Williams
Bammer will meet Vera Zvonareva, who accounted for fellow Russian Dinara Safina 7-5 6-3, in the last eight.
Next up for Jankovic is Li Na, who thumped 12th seed Shahar Peer 6-1 6-3, while Sharapova faces Denmark's Caroline Wozniakci.
"I played her in an exhibition match sometime back," Sharapova said of Wozniakci.
"She is an upcoming player and it should be a good match."
Serbian Ivanovic had damaged her left ankle when she slipped over on the baseline just four points before beating Olga Govortsova 6-3 6-1 on Wednesday.
However, she is hopeful of making next week's Dubai Open.
"The injury is not as bad as I thought. There is no fracture, it's an ankle sprain," said the world number three.
"But it is pretty painful and it is hard to step on it.
"I am definitely very disappointed. It's a disappointing way to end the tournament and I thought I was in good shape.
"Conditions were tough but I was happy with my game and I though I was playing well. I thought I was in with a chance of another title."
Williams made 40 unforced errors as she tumbled to defeat against Cibulkova, compared to just four by her 18-year-old Slovak opponent.
A delighted Cibulkova, who had never beaten a player ranked in the top 20 in the world before this week, said: "When I was little she was one of my idols, so I still can't believe it.
"I wasn't thinking who was on the other side, because I've lost to other good players just because of the name."