2024 Platinum
The 35-year-old Thompson, who qualified for the Volvo PGA Championship at Wentworth last summer, returned a two-under-par 68 around the tough Saunton links to lead the region's 15 qualifiers into the 72-hole championship at Southport & Ainsdale in mid-August.
There they will compete for the £78,000 prize fund which includes a cheque for £10,000 to the winner and a guaranteed place the Great Britain & Ireland team to play the United States in next year's PGA Cup - the club professionals' equivalent of the Ryder Cup, at The K Club in Dublin.
Thompson birdied three holes in a row from the second to give himself a flying start and then held on when the wind increased on the back nine to return the day's best card.
"I'd take a start like that anytime, especially around Saunton," said Thompson. "I'm very pleased and it gives me something to look forward to later in the season.
"I enjoy playing at Saunton and it's been good to me because the only time in recent years I failed to qualify for the Glenmuir finals was when the West Region competition was played on a different course."
Weymouth's Michael Watson can also start planning for a trip to Lancashire in August after his round of 69, one-under-par.
Among a five-man group sharing third place on level par 70 was Albert MacKenzie, the host club's professional, and Bristol's former European Tour winner Andrew Sherborne.