Kim Clijsters and Victoria Azarenka crashed out in contrasting styles at the BNP Paribas Open in India Wells.
Azarenka slumped to a 7-6 (7/4) 6-2 reverse at the hands of 28th-seeded Spaniard Maria Jose Martinez Sanchez, while the 14th-seeded Clijsters, who has made a strong return to the WTA Tour after coming out of retirement, had no answer to Russian 23rd seed Alisa Kleybanova, who posted a 6-4 1-6 7-6 (7/4) triumph.
Ninth seed Flavia Pennetta was another eye-catching casualty as Shahar Peer completed a three-set victory.
Italian Pennetta had battled back from a set down to win the second on a tie-break and take the match into a decider. But her 17th-seeded Israeli opponent broke four times in a dominant third-set display to complete a 6-4 6-7 (4/7) 6-1 triumph and set up a last-16 clash against Jelena Jankovic.
Sixth seed Jankovic was forced to play her best tennis in a near three-hour encounter with Italy's Sara Errani, who took the first set in convincing fashion.
Serbian Jankovic rallied to take the second on a tie-break before just edging a keenly contested decider for a 2-6 7-6 (8/6) 6-4 win.
Defending champion Vera Zvonareva, seeded 12th, advanced with a 6-2 6-3 win over Anastasija Sevastova of Latvia, while eighth seed Sam Stosur dropped just three games in disposing of Anastasia Pavlyuchenkova in 72 minutes.
The Australian was on top in the first set, a first-serve ratio of 63% helping her to a 6-3 success.
And she stepped up a gear in the second, winning 27 points out of 40 and converting all three of her break points to conclude a 6-3 6-0 win.
Spaniard Carla Suarez Navarro posted a 6-4 3-6 6-1 win over 27th seed Agnes Szavay of Hungary, while 13th-seeded Belgian Yanina Wickmayer saw off Italy's Roberta Vinci 6-1 3-6 6-3.