Rory McIlroy overcame what he thinks was a touch of sunstroke to move into a share of the halfway lead at the DP World Tour Championship in Dubai.
The World Number One shot a second round 67 and goes into the weekend 11 under par alongside World Number Two Luke Donald and Scot Marc Warren.
South Africans Louis Oosthuizen and Branden Grace are only a stroke behind.
"I got off the course yesterday and had a really sore head and a fever," said McIlroy. "I think it was a bit of sunstroke.
"I took a few things and felt better, but I'm not feeling great again. The sun's taking it out of me a bit."
He birdied two of the first three, but came up short of the green at the 245 yard fourth and bogeyed.
It was his only dropped stroke, however, and further birdies came at the seventh, tenth, 14th - he lipped out for eagle there - and 15th.
Overnight leader Donald had a 68, while playing partner Warren - 189th in the Official World Golf Ranking - matched McIlroy's round.
Earlier Sergio Garcia shot one of golf's most remarkable course records - two eagles, nine birdies, two bogeys and a triple bogey seven.
It all added up to a second round 64, eight under par, and from 49th place after his initial 73 he was back in contention at seven under.
Donald was one behind McIlroy and Warren playing the par-five 18th, but pitched to within 18 inches of the hole for a fourth birdie of the round and has yet to record a bogey in the tournament.
“Obviously I haven't dropped a shot in 36 holes so feel good about that,” said Donald, who won the Dunlop Phoenix in Japan last Sunday.
“I wasn't quite as good on the greens today; I had some opportunities, ten to 15 footers on a few holes that I just misread. But that was a solid round of golf.
“It was reasonably straightforward. I didn't put myself in too much trouble today, but certainly when I gave myself a little bit of trouble out on the course, I was able to recover with the putter.
“It's a great field in general and it usually produces a really exciting weekend. The last tournament of the year, we are looking forward to going out on a high note, and obviously Rory is playing well and a bunch of other guys are playing well, so should make for a fun weekend.”
Warren narrowly missed out on his home Aberdeen Asset Management Scottish Open title during the summer after leading by four shots with four holes to play, but is looking forward to the opportunity to try again for a first European Tour title since 2007 against the two best players on the planet.
“It was nice to be the Scot in that pack with the Englishman and the Northern Irishman,” he said.
“It's great to be in contention with guys like that, and looking down the leaderboard, it's a high-quality leaderboard and doesn't get any better anywhere in the world really.
“It's great for The European Tour and it's great for The Race to Dubai, and it's great to be a part of that.”