Britain's Andy Murray moved into the third round of the ATP and WTA Miami Open but Rafael Nadal, dizzy as he struggled to cope with the heat and humidity, retired from his match.
World number two Murray, twice a Grand Slam champion, downed Uzbekistan's 76th-ranked Denis Istomin 6-3, 7-5 to reach the third round in a night match.
"That second set was tight but I managed to get through it," said Murray, who next faces Bulgarian 26th seed Grigor Dimitrov in his quest for a third Miami crown.
Spanish fifth seed Nadal, a 14-time Grand Slam champion playing in the heat of the afternoon, feared for his safety and handed 94th-ranked Bosnian Damir Dzumhur a 2-6, 6-4, 3-0 triumph, stopping during a match for the first time in six years.
"Everything was fine until the end of the first set and I started to feel not very good," Nadal said. "It was getting worse and worse and worse.
"I get a little bit scared to be too dizzy and to lose fluids. I called the doctor a couple of times. I decided I was not safe. I wanted to finish the match but I decided I would not."
Two-time Slam winners Stan Wawrinka and Petra Kvitova crashed out of the hardcourt event, although Nadal's exit proved most stunning of all.
"Hopefully it's nothing," Nadal said. "Hopefully it's just the extreme conditions out there, the beginning of a virus combined with the conditions."
Nadal, a four-time Miami finalist but never a champion, was also a first-match loser at the Australian Open, only the second Grand Slam opener defeat of his career.
Dzumhur, 23, won 22 of the last 29 points as Nadal, 29, repeatedly spoke with a trainer, asking for his blood pressure to be taken after two games of the third set.
"Can we not check the tension, if it is good or bad please?" he said. Told it was good, he said, "Continue."
After dropping the third game, he sat with his head down as a trainer told him, "If you're feeling bad, there's no point to continue."
Nadal battled through three more points and finally said he could not go on.
"Definitely I want Rafa to recover," said Dzumhur. "He's one of the best players in tennis and I wish all the best for him."
World number one Serena Williams ousted Kazak Zarina Diyas 7-5, 6-3, in the match after Nadal and was also tested by the conditions.
"It was definitely humid," Williams said. "Rafa played before me. He was in the most intense part of the sun whereas I was on the tail end of it."
- Wawrinka, Kvitova fall -
Swiss fourth seed Wawrinka, who has won titles this year at Chennai and Dubai, was ousted by Russia's Andrey Kuznetsov 6-4, 6-3 while Czech eighth seed Kvitova, the 2011 and 2014 Wimbledon winner, fell to Russian 30th seed Ekaterina Makarova 6-4, 6-4.
Wawrinka, the 2014 Australian Open and 2015 French Open champion, managed only 16 winners against 37 unforced errors and went 0-for-8 on break point chances.
Kuznetsov, ranked a career-best 51st, avenged a third-round loss to Wawrinka at Indian Wells and made the Swiss his highest-ranked beaten foe.
With Nadal and Wawrinka out, the top-ranked player in their quarter of the draw is Canadian 12th seed Milos Raonic, coming off a runner-up showing at Indian Wells.
Raonic beat American Denis Kudla 7-6 (7/4), 6-4 and next faces US 22nd seed Jack Sock, who advanced 6-2, 3-2 when Ukraine's Sergiy Stakhovsky retired with a back injury.
The losses also mean highest-rated obstacles to Murray reaching the final are in his quarter of the bracket, Japanese sixth seed Kei Nishikori and French ninth seed Jo-Wilfried Tsonga.
- Nishikori, Kyrgios advance -
Nishikori advanced to the third round by downing 107th-ranked French qualifier Pierre-Hugues Herbert 6-2, 7-6 (7/4).
The 2014 US Open runner-up, coming off a fourth consecutive title at Memphis last month, next meets Ukraine's 27th-seeded Alexandr Dolgopolov.
Australian 24th seed Nick Kyrgios routed Cypriot Marcos Baghdatis 6-2, 6-1, to set a third-round date with 132nd-ranked US qualifier Tim Smyczek, who outlasted US 13th seed John Isner 6-2, 2-6, 7-6 (7/5).
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