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Andy Murray progressed to the Miami Open third round but Saturday's play was dominated by withdrawals, including fifth seed Rafael Nadal, and a curious end to Sam Querrey's challenge.
Second seed Murray was not at his fluent best again Denis Istomin but came through 6-3 7-5 to set up an enticing third-round clash against Grigor Dimitrov, a three-set winner over Federico Delbonis.
Nadal, by contrast, had to call a halt to his match against Bosnian Damir Dzumhur in the third set after suffering from dizziness in the humid conditions.
The Spaniard had comfortably won the opening set but Dzumhur led 2-6 6-4 3-0 by the time of the retirement.
"Everything was fine until the end of the first set," Nadal told atpworldtour.com. "Then I started to feel dizzy, not very good.
"It was getting worse and worse. Finally, in the second set, I realised that I could not keep playing.
"I wanted to finish the match, but I seriously could not. I stopped because I was concerned for my health."
He was far from alone, with Murray left as Great Britain's last representative in the men's draw after Aljaz Bedene pulled out with an apparent wrist injury when trailing Spain's Roberto Bautista Agut 7-5 2-2.
Sergiy Stakhovsky and 30th seed Thomaz Bellucci also retired from their respective matches against Jack Sock and Mikhail Kukushkin - adding to Roger Federer's withdrawal on Friday without playing, due to illness - but the strangest exit was Querrey's.
Serving to stay in the match at 4-5 in the third set against Adrian Mannarino, the American fell 0-40 down after a series of listless serves and wild backhands.
He was then issued a point penalty as a result, handing his opponent a 6-7 (5/7) 6-2 6-4 win without the need to even contest his three match points.
Fourth seed Stan Wawrinka was a high-profile casualty on a manic day in Key Biscayne, losing 6-4 6-3 to world number 51 Andrey Kuznetsov in just an hour and 19 minutes. Kuznetsov closed the match out with a love hold followed by a break to love.
John Isner also departed, the 13th seed beaten in a final-set tie-break by fellow American Tim Smyczek.
But there was straight-sets progress for the remaining seeds in action - Kei Nishikori, Jo-Wilfried Tsonga, Milos Raonic, Gael Monfils, Pablo Cuevas, Nick Krygios and Alexandr Dolgopolov.
Women's top seed Serena Williams claimed the 750th match win of her illustrious career, surviving a first-set test to beat Zarina Diyas 7-5 6-3.
Williams is seventh on the all-time list for that statistic on the WTA Tour, and will pass fellow American Lindsay Davenport for sixth should she reach the final this week at a tournament the Florida native has won eight times before.
Her next opponent on that quest will be Svetlana Kuznetsova after the 15th-seeded Russian beat France's Caroline Garcia 4-6 6-2 7-6 (8/6).
Fifth seed Simona Halep dispatched Julia Goerges 6-4 6-1 and will face Great Britain's Heather Watson, who battled from a set down to beat Yanina Wickmayer 3-6 7-5 6-3.
Agnieszka Radwanska enjoyed a routine 6-3 6-2 success against Madison Brengle to set up a clash with Timea Bacsinszky, who beat Ana Ivanovic 7-5 6-4.
Twelfth seed Elina Svitolina beat Caroline Wozniacki in a marathon last match of the day, winning seven straight points in a third-set tie-break to win 5-7 6-4 7-6 (7/1).
She will face Ekaterina Makarova, a 6-4 6-4 winner over eighth seed Petra Kvitova.
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