MacKenzies 8 Saturday on the par-5 18th left him tied for second with Brian Gay, two strokes behind Turnesa on the Annandale course. MacKenzie was penalized for moving impediments in the hazard while his ball was also in the hazard.
Turnesa, a PGA TOUR 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.
MacKenzie said he brushed them away with his hand, then he realized what he had done and told an official, who assessed the penalty.
Turnesa chased MacKenzie over the back nine with four birdies.
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.