Britain's Cameron Norrie was beaten by Taylor Fritz in the Miami Open third round as top seed Daniil Medvedev overcame leg cramps to advance.
Russia's Medvedev had cruised to a set and a 5-2 lead against Alexei Popyrin before he began to cramp in the heat.
Despite struggling to walk, Medvedev was able to secure a 7-6 (7-3) 6-7 (7-9) 6-4 win over the Australian.
"It's probably one of the sweetest victories in my career, because I was cramping like hell in the third set," Medvedev said.
"The only thing I was thinking about was not to fall down because if I fell down, I don't think I'd be able to get up.