Broadhurst thought his chance had disappeared when he bogeyed the final hole after driving into a bush to the left of the fairway.
But in the group behind, long-time leaders Barry Lane and Paul Lawrie made a mess of the 17th, Lane taking a bogey five and former Open champion Lawrie a triple-bogey seven.
That still left Lane needing only to par the 18th to win, but the 44-year-old amazingly crashed to a quintuple-bogey nine after also driving into a bush.
Attempting to hack out on to the fairway, Lane hit his second shot far too hard across the fairway to within a foot of the out of bounds fence.
From there he hit his third shot out of bounds and, after taking a penalty drop, hit his sixth shot short of the green.
Lawrie still had a 12-foot birdie putt to force a play-off but contrived to leave it short, leaving Broadhurst to claim the £144,000 first prize for his first victory since the 1995 French Open.
A closing 67 gave the 39-year-old a 13-under total of 271, one ahead of Lawrie with Portugal’s Jose-Filipe Lima chipping in for a birdie on the last to claim third. Lane had to settle for fifth place on eight under par after a closing 72.
“I thought I needed to birdie the 16th and par the last two holes,” revealed a stunned Broadhurst.
“I just wanted to set some sort of score but I was relying on Barry or Paul to make a mess of a hole somewhere along the way.
“When I drove into the bush on the 18th I thought that was it but as I was signing my card I saw Barry had driven into trouble. I still expected him to make a five and I was thinking about a play-off. You don’t wish what happened to him on anyone. I’ve done it myself enough times.”
Broadhurst, who was one of six players forced to complete their third rounds on Sunday due to Saturday’s rain delays, began the final round two off the lead and looked out of contention after bogeys at the third and fifth.
But, while all the attention was focused on playing partners Lane and Lawrie in the final group, he picked up birdies at the sixth, seventh and ninth and four more on the back nine to keep in touch with the leaders.
Broadhurst, who won both his matches in the 1991 Ryder Cup at Kiawah Island, suffered a serious hand injury in Dubai which kept him out for almost the whole of 2000, and lost his card the following season.
“You keep plugging away hoping it’s going to be your turn,” added Broadhurst, who regained his playing rights in 2003 and finished 44th on the Order of Merit last year.
“When I’ve won before my game has been in top order but on Wednesday I was really struggling and went out there with no expectations. Since 2000 it’s been a real rollercoaster but there have been signs the last couple of years that things are improving.
* Publication of the Golf 2005 supplement, due to appear in today’s Irish Examiner, has been deferred to Monday, April 11.