Graeme McDowell finished with a double-bogey six to lose the outright lead at the Ballantine's Championship in South Korea.
The Co Antrim player signed for an excellent third-round 66 at Pinx Golf Club on Jeju Island but it could have been better had he not overshot the 18th green.
That allowed playing partner Jeev Milkha Singh to draw level on 18-under par following an eight-under-par round of 64, which included a run of eight birdies in 10 holes. McDowell shot six birdies in his round.
Paul McGinley carded a second straight 67 and was four shots behind on 14-under, while Sweden's Johan Edfors birdied the last to complete a 69 and move to 13 under.
Open champion Padraig Harrington followed up a third-round 65 with a four-under 68 and was level with Australia's Kane Webber on 12-under.
The 28-year-old McDowell, from Portrush, led by two strokes halfway through the tournament following rounds of 68 and 64 and has lauded the 7,345-yard layout.
He flourished in the best of the conditions yesterday, carding the lowest round of the tournament in a second round delayed by high winds.
McDowell, whose season's best finish was fifth in the Dubai Desert Classic, is chasing a first European Tour victory since the 2004 Italia Open — his second triumph — and made a remarkable start with successive birdies on the par-four first and the par-three second.
McDowell then holed from 12 feet on the fourth for an eagle before successive birdies on the eighth and ninth and a further shot was claimed on the 13th. He then claimed a birdie on the par-five 16th before his first dropped shots since the first round on the final hole of the day.
McDowell missed the green and was forced to drop after going out of bounds.
McGinley was realistic about his chances.
"I felt I putted well again, but I lost ground," he said. "As I said yesterday, if I'm going to win I'm going to have to play really well — I've played well but not really well and tomorrow I'm going to have to play unbelievably well.
"All I can do is play as well as I can."
Fellow Dubliner Harrington was not surprised by the low scoring.
"The course was there for the taking — there's not too much wind — it was definitely on," he said. "I'm a long way behind. I was hoping to gain on the leader today, not fall further behind."