Ashleigh Barty got off to a hot start against Elina Svitolina but was ultimately beaten in straight sets in the round of 16 at the Miami Open.
The Australian 21st seed led 5-2 in the opening set but the Ukrainian fourth seed fought back to win 7-5 6-4 in a one hour and 20 minutes.
Svitolina defeated Barty's compatriot Daria Gavrilova in the previous round.
Venus Williams accounted for defending champion Johanna Konta 5-7 6-1 6-2 to reach the quarter-finals while a dominant Victoria Azarenka advanced with a straightforward win over Agnieszka Radwanska.
Three-times champion Williams, who turns 38 in June, stormed back from an early deficit to cruise past the British 11th seed, who needed several bouts of treatment on her lower back throughout a match that lasted two hours and 19 minutes.
Former world No.1 Azarenka, in only her second event after an eight-month absence because of a custody dispute involving her son, looked sharp throughout her 6-2 6-2 win over 30th-seeded Pole Radwanska.
Sloane Stephens raised her game to levels similar to last year when she won the US Open as she beat Spanish third seed Garbine Muguruza 6-3 6-4 and secure passage to the quarter-finals.
The American 13th seed dictated play against the Wimbledon champion from the start by taking eight of the first nine points of the match.
After securing a break in the fifth game of the second set, Stephens sent Muguruza packing with a backhand on the line on her second match point.
Stephens, who equalled her best result in Miami having also reached the quarter-finals in 2015, will next face German 10th seed Angelique Kerber, a 6-7 (7-1) 7-6 (7-5) 6-3 winner over Chinese qualifier Wang Yafan.
Fifth seed Pliskova, who reached last year's Miami semis, was first to reach the quarters after Zarina Diyas of Kazakhstan was forced to retire injured while trailing 6-2 2-1.
Former world No.1 Pliskova was efficient from the start and did not drop a point on her first serves in the entire match against Diyas, who took multiple medical time-outs and was visibly struggling with her movement.
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