Venus Williams edged Petra Kvitova in an Indian Wells Open thriller, while Naomi Osaka and Angelique Kerber moved through.
Williams overcame Kvitova in a blockbuster second-round clash at the WTA Premier event, where the Czech was one of six seeds to fall.
Osaka started her title defence in style, while Kerber and Karolina Pliskova also reached the third round.
But Caroline Wozniacki's struggles continued, the Dane joining Kvitova among the losers on Saturday.
WILLIAMS COMES THROUGH KVITOVA TEST
Williams recovered from a difficult start to get past Kvitova 4-6 7-5 6-4 after almost two and a half hours.
The American seven-time grand slam singles champion was the better of the two players in the third set and managed to break twice.
In what was just the seventh meeting between the two stars, Williams, 38, recorded her third win.
She will next face Christina McHale, who upset Russian 30th seed Anastasia Pavlyuchenkova 6-4 3-6 6-4.
SOME SEEDS SURVIVE
Of the 16 seeds in action, 10 managed to get through.
Kerber, the eighth seed, progressed impressively, dismantling Yulia Putintseva 6-0 6-2 in just over an hour.
Pliskova served 12 aces on her way to a 6-7 (4-7) 6-1 6-1 victory over qualifier Misaki Doi.
Danielle Collins, Belinda Bencic, Anastasija Sevastova, Anett Kontaveit, Julia Goerges, Aryna Sabalenka and Lesia Tsurenko also won through.
WOZNIACKI WOES CONTINUE AS KEYS EXITS
Wozniacki now has a 3-3 win-loss record this year after the 2011 champion slumped to a 7-5 2-6 7-5 loss to Ekaterina Alexandrova.
Playing on the WTA Tour for the first time since the Australian Open, Keys went down to Mona Barthel 3-6 6-1 7-5.
Donna Vekic and Carla Suarez Navarro also made second-round exits.