MIAMI (REUTERS) - Spaniard Rafael Nadal said dizziness prompted him to retire from his second-round match against Damir Dzumhur at the Miami Open on Saturday.

Sporadic boos greeted the 14-time Grand Slam champion when he called it a day during the third set in typically humid conditions in south Florida.

The 94th-ranked Dzumhur led 2-6, 6-4, 3-0 at the time, with the Bosnian 30-15 up on serve.

The last time Nadal quit during a match was in a quarter-final against Andy Murray at the 2010 Australian Open.

"Everything was fine until the end of the first set," Nadal said. "Then I started to feel dizzy, not very good. It was getting worse and worse.

"I wanted to finish the match, but I seriously could not. It was tough, because I felt I was playing well. I stopped because I was concerned for my health."

Before retiring, Nadal twice called for a trainer, and had his blood pressure checked on the second occasion, but resumed play both times after a short break.

Dzumhur was also affected by the heat early in the match and was the first to call a trainer, but he battled on and after a poor first set eventually gained control to post his first career victory against a world top-10 player.

Fourth seed Stan Wawrinka also bowed out on Saturday after the Swiss was sent packing 6-4, 6-3 by Russian Andrey Kuznetsov, who saved eight break points.

Sixth seed Kei Nishikori of Japan moved on after beating Pierre-Hugues Herbert 6-2, 7-6 (7-4).

Andy Murray takes on Uzbek Denis Istomin in the late match.