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 today.
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, 10th, 14th - he lipped out for eagle there - and 15th.
Overnight leader Donald had a 68, while playing partner Warren - 189th in the world - 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.
The score was all the more amazing with this being the 32-year-old Spaniard's first event since the Ryder Cup in September. He underwent laser surgery afterwards to correct his astigmatism.
"It was unbelievable, wasn't it?" he said after moving from one over par to seven under.
An 18-foot eagle putt from just off the back of the final green made Garcia the sixth player to hand in a 64 on the Greg Norman-designed Earth course, venue for the European Tour's season-ending showpiece for the past four years.
Garcia went for the surgery because he was finding contact lenses uncomfortable and said of his improved eyesight: "I'm still kind of getting used to it."
He had five birdies in an outward 31, started for home with two more, bogeyed the next two, then sank a 30-foot eagle putt on the long 14th.
The tee at the 371-yard 15th had been moved up and after driving the green he sank an eight-foot second putt for birdie, but then pushed an eight-iron into the water on the next.
With three putts a triple bogey went on his card, but he hit back with a six-iron to four feet and then had his closing eagle - after his drive had headed for the stream running down the fairway, but then hit the rocks and bounced out.
Moments earlier German Marcel Siem had hit his second shot into the water by the green and by taking a bogey six had to settle for a 65.
Welshman Jamie Donaldson also ran up a six and, having bogeyed the 16th as well, he dropped back from 10 under to eight under.