Barry Lane and Paul Lawrie shared the lead at 15 under par heading to the 17th, but both players hit their tee shots well left off the tee.
Lawrie took a penalty drop and eventually walked away from the hole with a triple-bogey leaving him at minus-12. Lane pitched out and hit his third short and left of the green. He two-putted for bogey to slip to minus-14, but that wasn't the last of his troubles.
Lane again drove into the left trees off the 18th tee at Quinta da Marinha Oitavos Golfe. The five-time winner on the European Tour played his second shot out of a bush. That shot flew way right and nearly out of bounds.
The 44-year-old had a restricted back swing for his third shot. He managed good contact, but the ball hit a rock and caromed out of bounds. Lane then took an unplayable lie penalty before he played his sixth shot short of the green. He left the final hole with a quintuple-bogey nine.
Lawrie, meanwhile, knocked his second shot to 25 feet at the last. He had a birdie try to tie Broadhurst at minus-13, but Lawrie's putt came up short and the title belonged to Broadhurst.
Lawrie ended alone in second place at 12-under-par 272 after a round of 70. Jose-Filipe Lima took third place at minus-11, while Richard Sterne ended alone in fourth at 10-under-par 274. Lane finished with a 72 to take fifth place at minus-9.
'With the 18th the way it is, anything can happen,' said Broadhurst, whose last win came at the 1995 Open de France. 'It's just a really tough finish the last two holes. I said to my caddy, 'if I can get in at 13 or 14 under, you never know.''
Broadhurst opened his round two strokes behind Lawrie, the third-round leader. Broadhurst fell further off the pace with bogeys at the third and fifth that dropped him to minus-7.
The Englishman fought back with consecutive birdies from the sixth. Broadhurst then birdied the ninth to move to 10 under. He kept climbing the leaderboard with birdies at 11 and 13.
Broadhurst jumped to 14 under par and within one stroke of Lane with back-to-back birdies from the 16th. The 39-year-old drove left off the tee at the 18th, pitched out and knocked his third to 25 feet. Broadhurst two-putted for bogey to end at 13 under.
'I started poorly and fell away and thought my chance had gone, but a strange thing happened on the 11th tee,' Broadhurst said. 'A Portuguese guy came up to me and asked if I was going to win this. I said, 'I don't think so, I'm four behind.' He says, 'I still think you're going to win.''
Lane and Lawrie went back and forth throughout the round atop the leaderboard. Lane birdied the third to tie Lawrie at minus-11. After Lawrie birdied the fifth, Lane again forged a tie for the lead at 12 under with a birdie at six.
Each player birdied the seventh, but Lawrie pushed one ahead with a birdie on the eighth. The first turning point came at 12 and 13.
Lawrie was unable to get up and down for par to drop back into a share of the lead at 13 under on No. 12. Lane ran home a 25-foot eagle putt at the next to move two clear of his playing partner.
Lane stumbled to a bogey on the 14th, while Lawrie birdied the same hole to create another tie. Lane bounced right back with a birdie on 15 and Lawrie joined him at 15 under with a birdie at 16.
Lawrie and Lane both struggled over the final two holes to fall out of the lead.