Pablo Larrazabal, the self-proclaimed “150th best player here”, completed a stunning four-shot victory at the French Open in Paris yesterday.

The smiling Spaniard, who came through 36 holes of qualifying to make it to the event at Le Golf National, entered the tournament ranked No481 in the world but walked away with a dream prize of £527,800 and entry to his first major - next month's Open Championship.

Larrazabal, 25, a rookie on the European Tour who, five years ago, was caddying for his brother in the event, opened with a 65 and led all the way, holding off Colin Montgomerie and Lee Westwood with a closing round of 67 for an aggregate 15 under par. Montgomerie, after easily his best display of the season, finished second with Westwood, who was third in the US Open two weeks ago, dropping to joint fifth after going in the lake on the last.

The winner, pitched into the lake during his celebrations, was overcome by his remarkable success. “I don't know how it feels - it's fantastic. I really played great golf and my putter was great all week,” Larrazabal said.

It was only the seventeenth tour event that Larrazabal had played, although his past experiences do include the Masters at Augusta - as a caddie for his brother, Alejandro, the Amateur champion in 2002.

Until this achievement he was only the fourth best-known golfer in his family - his parents were internationals. His father, Gustavo, made him work on a fish farm before turning professional to get an idea of what hard work is and learn the value of money.

His previous best finish was fifteenth and he had never before come within eight strokes of the winner. With this victory he will surge from 128th on the Order of Merit into the top ten and leap up more than 300 places on the world rankings.

Larrazabal, who played all week without a driver in his bag on the firm and bouncy course, started the final day three ahead and picked up three birdies in his first five holes. A double-bogey seven on the 9th cut his lead from five to two, but he had birdies at the next two. After taking six down the long 14th he ignored the dangers of the water to birdie the next two.

Montgomerie, giving his bid to save his Ryder Cup place a huge boost with a £351,867 cheque, took second from Soren Hansen, of Denmark, with a 40-foot closing birdie putt.

“That's a big step in the right direction,” the Scot said. “Forgive me for not knowing the winner's name, but he has a great future. Good luck to him. The flags were no gimmes on the last four and he played them in two under. It's difficult to win out here and he has done it very well.”

Westwood, who missed several crucial putts, said: “After the first five holes just about everything I tried turned to rubbish. What can you do? It was one of those weeks where nothing went right.”