Miami - Sloane Stephens powered past world No 3 Garbine Muguruza as the seeds continued to fall at the Miami Open on Monday.
US Open champion Stephens dominated Spain's reigning Wimbledon champion Muguruza to record a 6-3, 6-4 win and advance to the quarter-finals.
Stephens, the world No 12, will face Germany's Angelique Kerber for a place in the semi-finals.
Muguruza had been the highest ranked player left in the women's draw following the early exits of world No 1 Simona Halep and Caroline Wozniacki in the earlier rounds.
Meanwhile former world number one Kerber was made to sweat in her gruelling clash with China's Wang Yafan before prevailing 6-7 (1/7), 7-6 (7/5), 6-3.
Kerber's victory continues a remarkable run of results since the turn of the year.
The world No 10 has played six tournaments in 2018 and reached the quarter-finals or better in each event.
Earlier Monday, Czech fifth seed Karolina Pliskova booked her place in the last eight after opponent Zarina Diyas retired in the second set.
Pliskova was leading 6-2, 2-1 when the Kazakh player abandoned with an injury.