Green started the round seven shots behind Martin but birdied four of the first five holes at the Oceanico Victoria Club. He was at 9-under after 15 but two late bogeys meant he had to spend an anxious hour in the clubhouse to see whether his 18-under total of 270 would be enough.
“Coming from seven behind I knew I had to play the best round of golf I probably could and I had a 64 in mind,” Green said. “And when I got to 9 under for the day and 20 under and I thought I was in with a chance. But then I had a couple of bogeys which I thought left me short. But in the end a 65 was good enough and a win is a win.”
Martin, who held a three-shot lead going into the final round, stayed one stoke ahead by making a 15-foot birdie putt on the 12th. But he bogeyed three of the next four holes, before managing a birdie on the 17th. He then drove into the water on the final hole to finish with a double bogey for a 75 – putting him in a tie for sixth place.
Ryder Cup player Francesco Molinari of Italy came from even further back to finish in a four-way tie for second after a 10-under 62. Molinari, Robert Karlsson of Sweden (67), Joost Luiten of the Netherlands (69) and Gonzalo Fernandez Castano of Spain (68) were all two shots behind Green.
Molinari also shot a 62 in the second round but had 74s on Thursday and Saturday.
It was the second straight year that Martin wasted a chance for victory in the last round of the Portugal Masters. Last year, he partnered the eventual winner Lee Westwood in the final round but shot a 5-over 77.