Medvedev, the top seed, suffered leg cramps in the third set as the heat rose in Florida before closing out a 7-6, 6-7, 6-4 victory over the world number 86.

The Russian will play Frances Tiafoe for a place in the quarter-finals after the American fought back from a set down to knock out Serbian 16th seed Dušan Lajović 1-6, 7-6, 6-3.

"It's probably one of the sweetest victories in my career, because I was cramping like hell in the third set," said Medevdev.

"It's difficult to think about victory when you're cramping. 

"At the same time, I should have won in two sets and we would not be talking about cramping."

Finland's Emil Ruusuvuori, conqueror of third seed Alexander Zverev in the second round, is also through after he defeated Mikael Ymer of Sweden 4-6, 6-1, 7-5.

Ruusuvuori's next opponent will be Italy's 21st seed Jannik Sinner, who overcame 14th seed Karen Khachanov of Russia 4-6, 7-6, 6-4.

Fifth seed Diego Schwartzmann will play Adrian Mannarino of France for a place in the last 16 after he swept aside Yasutaka Uchiyama of Japan 6-3, 6-3.

In the women's draw, Tunisia's Ons Jabeur, the 27th seed, caused the upset of the day when she ousted American fourth seed Sofia Kenin 6-4, 4-6, 6-4.

Jabeur's reward is a round-of-16 clash with Sara Sorribes Tormo of Spain, who sent 21st seed Elena Rybakina of Kazakhstan crashing out of the tournament with a 6-1, 3-6, 6-2 win.

Japan's second seed and Australian Open champion Naomi Osaka progressed to the next round without having to hit a ball after opponent Nina Stojanović of Serbia withdrew due to injury.

The Women's Tennis Association 1000 and Association of Tennis Professionals Masters 1000 tournament continues tomorrow.