Sir Bradley Wiggins admitted he was felling the heat after maintaining his overall lead at the Tour of California.
Taylor Phinney sprinted clear for a 12-second victory in stage five but Wiggins finished in the main bunch to protect his 28-second advantage over nearest rival, Australia's Rohan Dennis.
"Everyone was really feeling it out there," said former Tour de France winner and four-time Olympic gold medallist Wiggins.
"That was the hottest day I've ever experienced on my bike. It was like being in an oven all day."
Wiggins and his Team Sky team-mates have another tough test to defend their yellow jersey in Friday's 151km sixth stage.
The route includes four tough climbs, including the most difficult profile of the race — the final 2km ascent to the Mount High ski area.
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