The Ryder Cup hopeful's 54-hole total of 12-under 198 leads Henrik Stenson (68) heading into Sunday's closing round when he seeks his 12th tournament crown.
"I had lots of chances and hit a lot of really good shots -- and a couple of poor ones, probably due to a lack of concentration," the Northern Ireland native said. "I can still play better (but) I'm playing with one of the great players in the world in Henrik again tomorrow, so it should be great."
Defending champion Ross Fisher (69) is 1-under 209 and joins eight others in a tie for 37th place.
First-round leader Rolf Muntz (69) is 5-under 205, good for a tie for 53rd place.