Lucas Bjerregaard appeared to be cruising towards a first European Tour title before a wobble at the end of the back nine blew the race for the Portugal Masters wide open.
The Dane, a shot clear overnight, carded four birdies in his first eight holes to race into a four shot lead.
However, he overshot his approach to the ninth and then miscued his chip, with the subsequent bogey seeing him turn in 32 to lie 17 under par at Dom Pedro Victoria Golf Course.
Bjerregaard has missed only five cuts this season but a lack of big finishes have left him 114th on the Race to Dubai Rankings presented by Rolex and needing a strong end to the campaign to retain his playing privileges.
Rounds of 66-65-68 put him a shot clear going into the final round in Vilamoura, and the 26 year old holed a ten foot birdie effort on the first.
A lovely pitch to eight feet set up a birdie on the fourth and Bjerregaard made it back-to-back gains by getting up-and-down from a bunker on the par five fifth.
Bjerregaard holed a 25 footer on the eighth, but then dropped a shot at the next to leave the door ajar.
Playing partner George Coetzee took full advantage, making his second birdie of the day from six feet on the ninth to get within two of the lead on 15 under.
He was joined by England’s Graeme Storm, who was four under through 11 after a hat-trick of gains from the ninth.
Storm had experienced a career low at this venue 12 months ago when he looked to have narrowly lost his European Tour card, only to be handed a reprieve when Patrick Reed failed to compete in the minimum number of events.
To the delight of the home fans, the clubhouse target was set by Portugal’s Ricardo Gouveia after a closing 65 gave him a 14 under total.
Bjerregaard responded with a birdie from 15 feet on the tenth, but Coetzee remained two behind by following him in from a similar distance.
However, Bjerregaard went three clear at the next after a brilliant approach to two feet.