Serena Williams and Agnieszka Radwanska exited the Miami Open on Monday, while Angelique Kerber survived a big scare to book her place in the quarter-finals.
Williams and Radwanska both won their first sets but lost out against Svetlana Kuznetsova and Timea Bacsinszky respectively.
German second seed Kerber looked certain to face the same fate in Key Biscayne, but recovered from losing the second set to knock out Timea Babos.
Garbine Muguruza was defeated by Victoria Azarenka, while Simona Halep made the last eight thanks to a straight-sets win against Heather Watson.
TOP SEEDS TUMBLE
World number one Williams was searching for a fourth consecutive title and ninth overall in Miami, but she was defeated 6-7 (3-7) 6-1 6-2 by inspired Russian Kuznetsova.
Second seed Radwanska looked to be cruising against Bacsinszky, taking out the first set, but the Swiss recovered to seal a 2-6 6-4 6-2 victory in just over two hours.
Muguruza took the fight to BNP Paribas Open champion Azarenka but the Spanish fourth seed came up short, going down 7-6 (8-6) 7-6 (7-4).
KERBER SURVIVES A BIG SCARE
The Australian Open winner appeared to be joining Williams, Radwanska and Muguruza as the big names to exit on Monday, but she recovered to limp past Babos.
Kerber sealed the first set in comfortable fashion, breaking twice, but went down in the second to the clinical Hungarian.
The German was then 3-0 down in the third set but she managed to dig deep to clinch the 6-2 3-6 6-4 victory and a clash against Madison Keys, who defeated Irina-Camelia Begu 6-3 6-1.
AZARENKA'S MOMENTUM IS BACK
Azarenka's victory over Muguruza was her ninth straight win, which included an Indian Wells triumph.
"I think it was a high-quality match for both of us. It was a lot of good striking, a lot of winners, and both of us taking opportunities," Azarenka said.
"I think today I served really well, and I played to win in important moments. Momentum shifting, I think I was a little better today."
HALEP, BACSINSZKY TO DO BATTLE IN QUARTERS
Halep will face Bacsinszky for a spot in the semi-finals, while it is an all-Russian quarter-final of Kuznetsova and Ekaterina Makarova.