Lee Westwood made the most of a favourable draw and some previous local knowledge to fire a bogey-free 62 in pursuit of a second Scottish Open title, 22 years after the first.
Westwood carded two eagles in the space of five holes and added five birdies to finish nine under par at the Renaissance Club, a shot ahead of Sweden's Alexander Bjork and Holland's Joost Luiten.
Scotland's Scott Jamieson headed the 15-strong home challenge on seven under, with compatriot Craig Lee another stroke back alongside England's Robert Rock and Finland's Kalle Samooja.
Three Australians are in a tie for eighth at five-under after Wade Ormsby, Lucas Herbert and Min Woo Lee carded rounds of 66.
The early starters were faced with cold, damp and windy conditions, but Westwood was among the afternoon wave who acknowledged they had benefited from considerably calmer and warmer weather.
"I opened the curtains this morning and thought, 'ooh, that looks rough'," said the 47-year-old, who won the Scottish Open at Loch Lomond in 1998.
“You've still got to make hay while the sun shines or the wind drops and I did that.” – Lee Westwood
"But that was the forecast, chilly and damp and then clearing up as the day went on.
"You've still got to make hay while the sun shines or the wind drops and I did that. You've got to be patient. If you're not three or four under early you can start chasing and getting aggressive. You have to break it down and play the course on its merits."
Westwood practised at the Renaissance Club in the week before finishing 13th in the US Open at Winged Foot and had plenty of other experience of the venue to draw upon from the time he lived in Edinburgh.
"I've played here loads of times," added Westwood, who won his 25th European Tour title in Abu Dhabi in January, the last Rolex Series event before this week due to the disruption caused by the coronavirus pandemic.
Defending champion Bernd Wiesberger carded an opening one-under-par 70, with playing partner Tommy Fleetwood a shot better off after recovering from two-over par after nine holes with four birdies on the back nine.
- Phil Casey, PAA