Graeme Storm compiled a back nine 32 to set the clubhouse lead at the Johnnie Walker Championship at Gleneagles.
The Englishman completed a 68 to set a target of 13 under par to those players still out on the course.
Storm dropped a shot at six and had to wait for the par five ninth before he made his first birdie.
But having regisstered one he then proceeded to pick up shots at the tenth, 11th and 12th on a day when no fewer than seven different players have held a share of the lead at some stage.
Storm birdied 15 and 16 to take the lead outright as overnight leader Gregory Havret faltered but a birdie at 17 dented his chances.
But Storm responded magnificently with a birdie at the last and clenched his fist to celebrate a fine round.
Sweden’s Peter Hanson earlier shot 69 to complete his four rounds in an 11 under par 281.
France’s Havret currently leads on 14 under par with two holes to play.
He birdied the second but dropped shots at the third and fifth as he looked to complete a wall-to-wall victory.
An eagle at the par five ninth and a birdie at 14 saw him reclaim the lead after the earlier players had moved ahead of him.
At the 15th - where the Frenchman had registered two double bogeys this week - Havret must have feared thw worst when his second shot found the bunker.
But he chipped to 12 feet and holed a steady putt to save par.
A birdie at the par five 16th put Havret back in the lead and he was just two pars away from victory.
