England's David Horsey fired a first-round 61 to seize the early lead in the Saudi International on Thursday, as US Open champion Bryson DeChambeau and world number one Dustin Johnson got off to solid starts.
Big-hitting American DeChambeau carded a five-under 65 to sit tied-fourth after the opening round, four shots behind, while Masters champion Johnson signed for a 67.
"I'm definitely very pleased. I was driving it a bit all over the place for the most part out there," said DeChambeau.
In a star-studded field, it was world number 282 Horsey who shone brightest on day one, rolling in nine birdies to sit at nine-under par, one ahead of Scotland's Stephen Gallacher.
He briefly threatened a 59 but, needing an eagle on the par-five 18th to post the magic number, could only manage a par.
"It's a shock actually," he said. "I've been playing rubbish the last couple weeks."
Former Ryder Cup winner Gallacher shot the lowest first round of his European Tour career in his 584th tournament with an eight-under 62.
The 46-year-old, who finished 173rd in the Race to Dubai last season, made 10 birdies in a sparkling performance.
"I couldn't wait for 2021 to come really and get back to a bit of normal -- back playing and back enjoying it," said the world number 501.
DeChambeau, who said earlier this week that he was "flattered" by proposed new rules to curb long tee shots, poured in seven birdies to set up a possible title tilt.
"I know that I can hit it far out here," he said.
"I'm disappointed it's not as far as I would like it but once I got out there and was hitting some wayward shots, you have to try to rein it in and control it better.
"I was able to do that for the most part and miss it in the right places and hopefully I miss it in the right places when I do hit it off-line."
Johnson, making just his second start of the year, won the inaugural Saudi International in 2019 before finishing runner-up to Graeme McDowell last year.
He struggled to find his best form on Thursday, but managed to stay bogey-free.
Paul Casey, who won last week's Dubai Desert Classic, opened with a 69.
Patrick Reed, whose victory last week at Torrey Pines on the PGA Tour was overshadowed by an 'embedded ball' controversy, also settled for a one-under round.
Austrian Bernd Wiesberger sits alone in third place on the early leaderboard after a 64.