Alvaro Quiros, with one win in Dubai already this year, emerged as the biggest threat to Rory McIlroy's hopes of ending The European Tour season with back-to-back wins - and maybe taking The Race to Dubai title as well.
The Spaniard finished a course record-equalling 64 by sinking a 20 foot eagle putt and will go into the third round of the Dubai World Championship presented by DP World four clear of the star-studded field on 12 under par.
McIlroy twice shared the lead on the back nine, but left a chip short of the green on the 17th and then bogeyed the last as well after driving into water.
Those errors dropped him into joint third with England's Robert Rock.
Northern Ireland's US Open Champion, who came from behind Quiros to win the UBS Hong Kong Open last Sunday, has to triumph again to have a chance of denying Luke Donald The Race to Dubai crown.
Even then Donald would complete his double of European and US PGA Tour money list titles if he finishes in the top nine this weekend and thanks to three closing birdies he is in a tie for 12th at halfway.
McIlroy knows all about Quiros - not just from last week, but also from the Omega Dubai Desert Classic in February. The 22 year old was joint leader with a round to go, but fell back to tenth as golf's biggest-hitter came charging through.
This time Quiros resumed four behind Peter Hanson, but with the Swede struggling and Scot Paul Lawrie wasting a red-hot start the opportunity was there.
He turned in 33 with birdies at the second, fourth and eighth and then stepped it up even more on the inward half.
After further birdies at the 11th, 14th and 16th he took advantage of the tee being moved forward 95 yards on the par five last.
McIlroy has been suffering from a virus for the past few weeks and has now been told he might have been battling with dengue fever, transmitted by a mosquito bite and fatal in less than one per cent of all cases.
"It could have been a number of things and I'm going to see a doctor again tomorrow before deciding whether to go to Thailand next week," he said.
"To be honest, I'm ready for the season to be done and looking forward to putting the clubs away."
Donald was down in 31st place when he three-putted the eighth, but after pars on the next seven holes he made 15 foot putts on the 16th and long 18th and in between holed from ten feet.
"Just personally in terms of my mental approach, that was huge," said Donald.
"It would be foolish of me to rely on him (McIlroy) not winning. I know what's at stake and it's a big deal to me.
"I was frustrated out there. I tried to stay patient, but it's tough. I want to finish off what I came here to do and those last three brought a smile to my face.
"There's certainly a lot of pressure. I'm still making a few mistakes - maybe because of what's at stake. When there's a lot on the line you feel more nervous, but sometimes it's a good thing."
Quiros said: "Obviously they are fighting for The Race to Dubai final top position, but we are playing here to try and ruin the party.
"They are not the only important people in the golf tournament."
Hanson shot 72 and Lawrie's 73 - a big disappointment after three birdies in the first four - dropped him to joint seventh.