Simona Halep claimed her fourth successive win over Venus Williams to reach the Miami Open quarter-finals.
The Romanian third seed hit 21 winners as she beat Williams 6-3 6-3 and faces the winner of an all-Chinese match between Wang Qiang and Wang Yafan next.
Either Halep or Petra Kvitova could replace Naomi Osaka as world number one at the end of the tournament.
Czech Kvitova beat France’s Caroline Garcia 6-3 6-3 to reach her fifth WTA quarter-final of the year.
The second seed will play Ashleigh Barty next after the Australian fought back to beat Kiki Bertens 4-6 6-3 6-2.
Osaka will remain at the top of the rankings unless Halep or Kvitova reach the final.
If both players make the final, then the winner will claim the number one ranking.
Romanian Halep was world number one for 48 weeks before being replaced by Osaka in January, while two-time Wimbledon champion Kvitova has never held the top ranking.
Canadian teenager Bianca Andreescu’s 10-match unbeaten run came to an end as she retired with injury.
The 19-year-old trailed Estonia’s Anett Kontaveit 6-1 2-0 when she withdrew with a right shoulder problem.
Hsieh Su-wei, who knocked out top seed Osaka on Sunday, continued her good form with a three-set win over Caroline Wozniacki.
The Taiwanese beat the Danish former world number one 6-3 6-7 (0-7) 6-2 and will play Kontaveit in the last eight.