Australia's Robert Allenby has lost his lead at the Dubai World Championship as Englishman Lee Westwood capitalised on a day of amazing twists and turns.
Westwood leads by two at halfway after a second round 69, but only thanks to late errors by current Order of Merit leader Rory McIlroy and then Padraig Harrington.
Twenty-year-old McIlroy led by two after a dazzling front nine 31, but three-putted the 14th and 15th in coming home in 38.
That left Harrington in front, but he put two balls in water on the 620-yard final hole at Greg Norman's new Earth course.
The three-time Open champion came off with a double bogey seven before Westwood birdied the same hole to double his advantage.
After an impressive 65 in the opening round Allenby could only manage a disappointing even-par 72 and is joint second with McIlroy, Harrington, England's Ross McGowan, Colombian Camilo Villegas, and South African Louis Oosthuizen.
Geoff Ogilvy improved to a tie for 12th place at five-under following his 69, while Scott Strange is a further stroke behind.
Meanwhile, Adam Scott dropped down to a tie for 20th after a 73.
It was a real tale of two halves for McIlroy as the battle for the No.1 spot moved closer to becoming a two-horse race with Martin Kaymer down on two-under and Ross Fisher level par, both after 71s.
An eagle and three birdies swept McIlroy from three behind to two in front, but he failed to capitalise coming home.
"I'm still in a good position," he said.
"I felt like I played the back nine okay, but it was just those two short putts."
Both the par putts he missed were from three feet.
Westwood led by two himself after matching McIlroy's two opening birdies, but bogeyed the eighth and did not have another birdie until the 16th.
Kaymer is out of the reckoning if he fails to finish in the top four, while Fisher needs to be first or second on Sunday - his 29th birthday.
Both were disappointed with rounds of 71 and both revealed themselves as no great fans of the lay-out.