Rory McIlroy opened a six-shot lead over title rival Luke Donald after day one of the Dubai World Championship.
The Northern Irishman must win the tournament and hope Englishman Donald finishes outside the top nine to end the year top of the European rankings.
McIlroy carded a double bogey on the second hole but six birdies on the back nine propelled him to six under par, two behind leader Peter Hanson.
Donald hit three bogeys in a row to finish on level par and is equal 26th.
After the first nine holes US Open champion McIlroy, having found the bushes on the second hole, was three behind playing partner Donald and seven shots off the lead.
But Donald, who has the chance to become the first golfer to win both the European and American money titles, hit a drive left into the bushes on the 14th and had to chip out to safety before dropping a shot.
The world number one followed that slip with two bogeys on 15 and 16.
McIlroy, who won in Hong Kong last week, started his revival with a birdie on the 10th and finished with a flurry, carding five birdies in his last six holes.
The 22-year-old said, still suffering from a virus and awaiting blood test results, said: "It's sort of taken the pressure off. I'm not 100% and there's nothing I can do about it.
"I made three silly mistakes on the front nine but stayed patient and the back nine was pretty much flawless.
"I definitely don't feel invincible, but I feel every time I tee it up I have a good chance of shooting a good score.
"It was the perfect start for me and really sets me up for the next three days. I didn't expect Luke to play the way he did."
Donald said: "I hit a few loose shots. They came out of the blue a little bit, although there were a couple of times last week when I had that left shot and I've got to keep working on it.
"I felt very much in control and then I lost it, but this course can do that to you. There are a lot of hazards in the middle of fairways, so you aim for one side and if you miss it you can be in the bushes."
Swede Hanson equalled Lee Westwood's course record to lead on eight under, with Scotland's Paul Lawrie second on seven under, one ahead of McIlroy.
Sergio Garcia, chasing a third successive European Tour win, is fourth after a 67.
World number three Westwood managed a one-over-par 73, which included a double bogey on the short 13th after he had to play his second shot left-handed from the side of a bunker.