Russia's Daniil Medvedev is two wins away from regaining the men's world number one spot after reaching the Miami Open last 16.
Medvedev ended Novak Djokovic's long run at the top of the rankings last month 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.
The US Open champion moved into the fourth round with a 6-3 6-4 win over Spain's Pedro Martinez.
"I think in general I played not so bad, they are really slow courts here so playing against a Spaniard is not easy," said Medvedev, who has not reached the Miami semi-finals in his previous three main-draw appearances.
"I felt like we had a lot of rallies where he was bringing the pace down in the point and I couldn't do much.
"I tried to serve well, keep consistent and make less errors in the most important points."
Medvedev will play American world number 39 Jenson Brooksby, who beat Spain's Roberto Bautista Agut, next.
British number one Cameron Norrie, seeded 10th and the nation's final representative in the draw, will face sixth seed Casper Ruud of Norway in the last 16 on Tuesday.
Phone: (800) 737. 6040
Fax: (800) 825 5558
Website: 
Email: 
