Stephens shows class to stun Muguruza as Konta exits
US Open champion Sloane Stephens upset Spanish third seed Garbine Muguruza 6-3 6-4 to reach the Miami Open quarter-finals, while Czech Karolina Pliskova advanced when her opponent retired hurt.
Stephens, who raised her game to levels similar to last year when she captured a maiden Major title in New York, dictated play against the Wimbledon champion from the start.
The American 13th seed raced out of the gate 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 (1) 7-6 (5) 6-3 winner over Chinese qualifier Wang Yafan.
Venus Williams knocked out Britain's Johanna Konta, 5-7 6-1 6-2 in a thrilling contest to make the quarter-finals.
Konta had received treatment during a medical time-out at the end of the second set.
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.
Nick Kyrgios, meanwhile, produced another blistering performance to reach the last-16 in the men's event.
Kyrgios did not face a break point and needed just 66 minutes to see off Italy's Fabio Fognini 6-3 6-3 in round three.
As a final backhand from No.11 Sam Querrey's racquet dropped into the net, Canadian Denis Shapovalov pointed at his left forearm and yelled: "I've got ice in my veins!"
Just four days after saving match point in a third-set tie-break in his opener, the 18-year-old defeated Querrey 6-4 3-6 7-5 to advance to the last-16 on his debut at the event.