Simona Halep maintained her fourth successive win over Venus Williams to reach the Miami Open quarter-finals.
The Romanian third seed hit 21 champions as she overcome 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 can 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 year.
The next seed will play Ashleigh Barty following the Australian fought back to beat Kiki Bertens 46 6-3 6-2.
Osaka will remain on top of the rankings unless Halep or Kvitova hit the final.
If both players make the ultimate, then a winner will claim the number one standing.
Romanian Halep was world number only for 4-8 weeks before being substituted by Osaka in January, while twotime Wimbledon champion Kvitova never held the top ranking.
Canadian teen ager Bianca Andreescu’s 10-match unbeaten run came to an end because she retired with trauma.
The 19-year-old trailed Estonia’s Anett Kontaveit 6-1 2-0 when she withdrew with the right shoulder problem.
Hsieh Su-wei, who knocked out top seed Osaka on Sunday, continued her good form using a three-set win over Caroline Wozniacki.
The Taiwanese beat the former world number one 6-3 6-7 (0-7) 6-2 and can play Kontaveit from the previous eight years.