Russia's Daniil Medvedev is two wins away from regaining the men's world number one spot after reaching the Miami Open last 16.
Poland's Iga Swiatek, who will become the new women's world number one after Ash Barty's retirement, earned her 14th straight win by beating Coco Gauff.
Japan's Naomi Osaka also reached the quarter-finals with victory against American Alison Riske.
Last month, Medvedev ended Novak Djokovic's long run at the top of the rankings before the Serb moved back ahead.
But with Djokovic absent in Miami, the 26-year-old Russian will take over again if he reaches the semi-finals.