Rafael Nadal was forced to retire as the heat proved too much for the Spanish fifth seed at the Miami Open on what was a mixed day for the seeds.
Andy Murray, Kei Nishikori and Milos Raonic all progressed as expected into the third round, but they will not be joined by the likes of fourth seed Stan Wawrinka and fellow seeds John Isner and Nadal.
Murray won a tough match against Denis Istomin, while Jo-Wilfried Tsonga cruised against Santiago Giraldo.
Nick Kyrgios also lived to fight another day after seeing off Marcos Baghdatis, while 16th seed Gael Monfils was too good for Tatsuma Ito.
MURRAY PERSEVERES, NISHIKORI CRUISES
Murray did not have it all his own way against Istomin but progressed after a 6-3 7-5 win, saving four out of five break points in the process.
Istomin tested Murray with his serve but was also wasteful, striking five aces and six double faults, while winning just 30 per cent of second serve points.
Nishikori saw off Pierre-Hugues Herbert 6-2 7-6 (7-4) in just under 90 minutes, despite being beaten by nine aces and serving up four double faults.
Raonic saw off Denis Kudla 7-6 (7-4) 6-4, even though Kudla won 88 per cent of points on his first serve, while Tsonga smashed Giraldo 6-3 6-1 in just over an hour.
Kygrios and Monfils progressed in straight sets, with the pair triumphing 6-2 6-1 and 6-3 6-2 over Baghdatis and Ito respectively.
NADAL RETIRES, WAWRINKA SECOND-BEST
Fourth seed Wawrinka and Nadal headlined the round two exits.
The Swiss world number four was out played in the hot conditions as Andrey Kuznetsov progressed courtesy of a 6-4 6-3 loss, sending down seven aces and winning 84 per cent of first serve points in the process.
Nadal won the first set 6-2 but lost the second 6-4 before retiring due to dizziness while trailing 3-0 in the decider.
Isner, Sam Querrey and Thomaz Bellucci were the other seeds to exit on Saturday.
UNBREAKABLE BIG NAMES
The big boys came up with the big points as the likes of Murray, Tsonga and Kyrgios all proved hard to break in their straight-set wins.
It was not for a lack of trying on their opponents' behalves.
Istomin forced five break point opportunities against Murray, but only converted one, while Baghdatis had the same ratio against Kyrgios.
Tsonga faced three break points against Giraldo and saved all three.
MURRAY UNHAPPY, NADAL FEELS HEAT
Murray was less than pleased when in the fifth game of the second set he realised he was serving with a ball from a women's match.
"Not good enough," he told the match umpire. "Completely unacceptable."
Meanwhile, Nadal explained his premature exit: "Finally, in the second set, I realised that I was not able to keep playing. I tried to resist, but I got a little scared to be too dizzy and lose."
World number one Novak Djokovic is back in action as the seeds face off on Easter Sunday.
Djokovic takes on 33rd seed Joao Sousa, while Tomas Berdych will meet American Steve Johnson.
Elsewhere, eighth seed David Ferrer will play Lucas Pouille.