Edoardo Molinari was the early pace-setter as The Barclays Scottish Open began at Loch Lomond thanks to an eagle two at the 14th.
The World Number 41 from Italy started his round at the tenth and was level par when he holed out his approach at the 371 yard par four hole.
And four further birdies - along with a dropped shot at the 18th - left the former Challenge Tour Number One five under with four to play.
That was one stroke better than England's Graeme Storm and Scot Stephen Gallacher.
Storm - 11th at last week's Alstom Open de France - opened with a back nine 34 but three birdies in four holes from the third sent him into a tie for second with three to play.
Gallacher recently recorded three top-ten finishes in a row on The European Tour and his good form continued as he advanced to four under with four to play, one ahead of BMW International Open winner David Horsey and Swede Mikael Lundberg.
