A wild approach at the 18th hole cost Graeme McDowell the outright lead after the third round of the US $ 2.9 million Ballantine's Championship in Jeju, South Korea on Saturday.
A double-bogey six gave the Northern Irishman a six-under 66, leaving him tied with India's Jeev Milkha Singh on 18-under 198 in the first European Tour event to be held in South Korea.
Singh fired a sparkling 64 in calm conditions on the honeymoon island of Jeju following two days of gusting winds.
Ireland's Paul McGinley carded a 67 to claim third position four strokes off the pace at the cliff-top Pinx Golf Club while British Open champion Padraig Harrington was a further two adrift.
Resplendent in a pair of bright pink trousers, McDowell continued his red-hot form as he tore up the front nine in 30 shots.
Four birdies and an eagle on the par-five fourth, where he sank a 20-foot left-to-right putt, put him firmly in the driving seat with only Singh posing a serious threat.
The Indian rattled off five successive birdies from the seventh and kept the pressure on McDowell as the two men went toe to toe in an absorbing duel.
McDowell claimed further birdies at 12 and 16 before overcooking his approach to the 18th and having to drop for a penalty stroke after finding a lateral hazard.
"When Jeev made five birdies in a row I knew I had a fight on my hands," McDowell told reporters. "Obviously it was very disappointing to finish like that.
"It's a wake-up call but it doesn't change my outlook. I still have to do the business tomorrow. Jeev is going to be very hard to shake off."
McDowell, who returned a 64 on Friday, is chasing his third victory on the European Tour, his last win coming at the 2004 Italian Open.
But Singh believes he has the momentum going into Sunday's final round.
"Today was one of those days when I felt I couldn't miss," said the Indian, who arrived here semi-concussed after crashing his golf buggy into a palm tree at last week's Malaysian Open.
"I had no idea I made five birdies in a row. I knew I'd made a few. I wasn't thinking about it. It was just the momentum."
Irishman Harrington chipped in at the 18th for a 68 which tied him for fifth place on 204 with Australian Kane Webber (65).
"It was nice to chip in but obviously I hoped to gain on the leader and not fall further behind Graeme," said Harrington. "No matter what I do tomorrow it's out of my hands which is a pity."
Sweden's Johan Edfors (69), who played in the final group with McDowell and Singh, finished fourth, one shot ahead of Harrington and Webber.
World number five KJ Choi failed to mount a charge in front of his home fans, firing his second successive 69 for a total of 209.