The Northern Ireland ace — who hasn't won since the Dutch Open in 2008 — hit six birdies in a bogey-free round to lead the way on a day of low scoring at Loch Lomond.
He tops the leaderboard by a stroke from Italy's Edoardo Molinari, Ireland's Damien McGrane and England's Graeme Storm.
The 42-year-old gave a hint that he was on the way back by winning the JP McManus pro-am earlier this week and was delighted to continue the run.
"I was delighted with the round," said Clarke.
"It was good to play well again. I have been working hard and doing the right things, but I wasn't holing the putts. But I changed my set-up after a chat with my caddy Brendan last Thursday night in Paris. And I've started rolling it better.
"Obviously winning this week has given me confidence and I'm a confidence player. I'm not playing that much differently — it's just that I'm holing a few putts."
And he reckons help from countrymen Graeme McDowell, who won the US Open last month, and Rory McIlroy has inspired him during his recent drought.
"I am delighted to see their success," he said.
"It's great for European and Irish golf. Maybe I have been there for them in the past and now they are returning the complement to me. They've been telling me to keep going and encouraging me. But its what you would expect from those two guys."
John Daly, wearing typically garish trousers, is a stroke further behind the trio in second place after describing his opening eight holes as the best he has ever struck the ball.
The American has had well documented personal problems in the past and currently owes around one million dollars to the taxman.
But he is focussed on his game, looking slim and fit and confident he can mount a challenge this week.
He said: "I played real solid and the first eight holes were the best ball striking I can remember. I hit a lot of fairways and it was a nice start, something I've not done a lot of."
Joining Daly on four-under are Thailand's Thongchai Jaidee, home favourite Stephen Gallacher, Wales' Bradley Dredge, Japan's Ryo Ishikawa and Sweden's Peter Hedblom.
A further eight players -— including Francesco Molinari, India's JM Singh and England's Mark Horsey — are a further shot behind after carding three-under par 68s.
Ernie Els looked like he was on his way to a sensational score when he birdied four holes in a row on the front nine. But he failed to build on the momentum and two dropped shots after the turn saw him finish at two-under.
It was a disappointing afternoon for Phil Mickelson in his bid to secure a top-two finish which would see him overhaul Tiger Woods at the top of the world rankings.
After a solid start, the American, who was a runner-up at Loch Lomond in 2007, found trouble after a wayward tee-shot at the 14th which led to a double bogey.
The 40-year-old recovered with a birdie at the last to end the day with a level par 71.
