American Justin Thomas made a strong start at the 152nd Open but then hit trouble as rain squalls kept a grip on the early scoring at Royal Troon in Scotland on Thursday.

Sweden's Alex Noren was the early clubhouse leader with a birdie on the 18th giving him a two-under-par 69, but Thomas initially looked like eclipsing that mark.

The former PGA Championship winner gathered four birdies with one bogey on his outward nine and then birdied the 10th to top the early leader board on four under.

But a double-bogey six at the 12th and a bogey on the 13th dropped him back into the pack.

Fellow American Bryson DeChambeau, last month's US Open champion, started in the company of young Swede Ludvig Aberg, who is ranked fourth in the world, but the big-hitting DeChambeau suffered a terrible start.

He was five over after his first six holes and in danger of playing himself out of contention on day one. (Reuters)