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 (Thursday) 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."