MADISON, Miss. -- Will MacKenzie simply "spaced out" on the last hole.
Penalized two strokes for moving impediments in a hazard, MacKenzie lost three shots on 18 to give the Viking Classic lead back to Mark Turnesa.
MacKenzie's 8 Saturday on the par-5 18th left him tied for second with Brian Gay, two strokes behind Turnesa on the Annandale course.
"I made a huge mistake," MacKenzie said. "A very costly mistake."
Turnesa, a PGA Tour rookie who also topped the second-round leaderboard, shot a 6-under 66 for a 17-under 199 total. MacKenzie and Gay had 67s.
MacKenzie, who has one tour victory, the Reno-Tahoe Open in 2006, opened with birdies on the first two holes and made the turn at 32. His only stumble before 18 was a bogey on the fourth hole.
MacKenzie said he "spaced out" after a day of being able to lift, clean and place his ball because of wet conditions. There were a a few blades of grass near his ball, not anything that would be a problem, he said.
"There was a little clump of grass, like trimmings," MacKenzie said. "It wasn't enough to hurt my shot. I'm just anal about picking up around my ball for some reason."
MacKenzie said he brushed the grass away with his hand, then he realized what he had done and told an official, who assessed the penalty.
"Golf is a game you've got to tell the truth or it will come back and kill you," he said. "I called the rules officials over and said, 'I think I touched inside the hazard, what's going to happen?'"
Turnesa chased MacKenzie over the back nine with four birdies, but doubted he would be able to catch him with the round MacKenzie was having.
"I think I peeked at the leaderboard," Turnesa said. "I had just made a few birdies, and I thought I would have a one next to my name. Then I looked again and I was two back."
Turnesa, whose best finish this year was a tie for 22nd, led the Stanford St. Jude Championship after two rounds, then shot 70-77 and finished 37th.
The Viking Classic is the opening of the Fall Series in which players have seven events to improve their standing on the tour and attempt to finish in the top 125 money winners to secure playing privileges for next year.
Turnesa ranks 169th on the money list with $263,000. MacKenzie is 178th with $235,997. The winner this week will earn $648,000.
"I know that if you win, you get a nice big check," Turnesa said. "You want to win, that's for sure."
Turnesa and MacKenzie were paired for Sunday.
For MacKenzie the biggest problem would be not to brood about what happened on 18.
"Sometimes playing from behind is good," he said. "But I definitely wanted to be in the lead.