Australian Jason Day, feeling much better after tweaking his medication routine, coped with sizzling afternoon heat to move within one stroke of the lead after the second round at the $US6.5 million ($A8.08 million) HP Byron Nelson Championship on Friday.
Day parred the first six holes, before jump-starting his day with an eagle at the par-five seventh, where he crafted a seven-iron from the left rough and then took advantage of a lucky bounce by holing an eight-metre putt.
He added three birdies in four holes from No.10, before parring home for a bogey-free five-under 65.
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"It just seemed like a very long day, especially in the heat," said Day, who is alone in third place on nine-under 131.
"I stayed really patient and holed a lot of good putts to save par and keep the momentum going."
Americans Cameron Beckman matched the course record of 61 to share the lead with compatriot Blake Adams (64) at 10-under.
It was a good day for the Australians, 10 of whom made the cut.
Day is best placed, while Steve Elkington is also lurking close, two strokes behind, and Marc Leishman trails by four.
Day felt lousy on Thursday due to medication he started taking earlier this week for an apparent sinus infection.
But he phoned his doctor after the first round and was told to take his two daily pills at different times, rather than together.
"I feel much better today," he said. "I got a lot of sleep last night and had an easy morning, although I've still got blocked ears and nose and can't smell properly."
Elkington, meanwhile, used finesse rather than brute strength to compile his second straight 66.
"This course is like playing pool, "said the 47-year-old.
"You've got to have a good angle. If you don't, the course is very tricky.
"It's not on the greatest piece of land because it's squashed in here, but it's been able to hold great tournaments for a long time and it's got great closing holes."
Elkington has won 10 times on the US Tour, including the 1995 PGA Championship, but he has not tasted victory in more than a decade and is not fully exempt this year.
