Serena Williams was made to work hard before reaching the last 16 of the Nasdaq-100 Open on Sunday as the top names progressed in Miami.
Williams had to fight for her 6-3 6-3
win over Israel's Shahar Peer, while Amelie Mauresmo, Maria Sharapova and Elena Dementieva also came through.
"She was really gutsy," said Williams. "She gets a lot of balls back."
Justine Henin-Hardenne beat Nuria Llagostera Vives 6-3 6-2 and Kim Clijsters beat Nathalie Dechy 6-0 6-2.
Top seed Mauresmo made it through with a 6-2 6-1 win over Anna Smashnova, while fourth seed Dementieva eased past 27th seed Magdalena Maleeva 6-3 6-4.
There were minor upsets, with 13th seed Elena Bovina falling to France's Tatiana Golovin and 11th seed Patty Schnyder losing to Catalina Castano.
Japan's Shinobu Asagoe also scored a surprise 6-0 6-3 win over 14th seed Francesca Schiavone of Italy.
Asagoe will now face Wimbledon champion Maria Sharapova in the next round after the Russian beat American Marissa Irvin 6-2 6-0.
Eighth seed Venus Williams talked up her performance after thrashing Colombian Fabiola Zuluaga 6-2 6-0.
"The scoreline didn't show the intensity with which I had to play to get that scoreline," said Venus. "She's a great player."