Top seed Angelique Kerber barely raised a sweat as she raced past qualifier Risa Ozaki to reach the Miami Open quarter-finals, while Karolina Pliskova also booked a spot in the last eight.
World number one Kerber steamrolled Ozaki in straight sets at the WTA Premier event on Monday.
Czech second seed Pliskova withstood a late charge to beat compatriot Barbora Strycova, while Simona Halep overcame Samantha Stosur.
However, fellow seeds Dominika Cibulkova and Garbine Muguruza failed to progress.
KERBER SHOWS NO MERCY
The two-time grand-slam winner posted a comprehensive 6-2 6-2 victory.
Kerber claimed six breaks of serve as she hit 17 winners against the Japanese qualifier.
Standing in the way of Kerber and the semi-finals is Venus Williams, who saw off Svetlana Kuznetsova 6-3 7-6 (7-4).
PLISKOVA HOLDS OFF STRYCOVA, HALEP RALLIES
The quarter-finals beckon for Pliskova, who won 6-1 6-4.
Strycova produced a late charge but it was not enough as Pliskova reached the last eight of the tournament for just the second time.
It does not get any easier for Pliskova as Mirjana Lucic-Baroni awaits.
Lucic-Baroni, who beat Pliskova in the quarter-finals of the Australian Open, was too strong for Bethanie Mattek-Sands 7-5 6-4.
Romanian third seed Halep came from a set down and fended off a match point in her 4-6 7-5 6-2 win over Stosur.
The thrilling contest lasted two hours, 10 minutes in Miami.
CIBULKOVA, MUGURUZA DEPART
World number four Cibulkova was sent packing from the tournament after losing 7-6 (7-5) 6-1 to Lucie Safarova.
Spanish sixth seed Muguruza lost the opening set 7-6 (7-1) before retiring against Caroline Wozniacki.
Wozniacki will now lock horns with Safarova.
Meanwhile, Johanna Konta was too good for Lara Arruabarrena 7-5 6-1.