Monasterio posted a 4-under 67 to finish the event at 10-under-par 274. He won by a shot over Martin Maritz, who shot an even-par 71, and overnight leader Henrik Nystrom, who struggled to a 2-over 73.
The win was not Monasterio's first ever as he titled on the Challenge Tour last year. He played on that circuit primarily in 2006 without much success as he is 37th on the money list with three top-10s.
Now, he's a member of the European Tour for the remainder of the 2006 season and all of the 2007 campaign.
'I was having a good season, but now it has become a great season,' said Monasterio. 'Now I am European Tour member and I hope that this is only the beginning for me.'
Nystrom was the leader by two to start the round, but double-bogeyed the first. Monasterio steadily moved up the leaderboard with three birdies, an eagle and a bogey on the front nine. By the time he made the turn, Monasterio was tied with Maritz for the lead at minus-10.
Monasterio birdied the 14th to move one ahead at 11 under par. He dropped a shot at 16 to fall back into a tie, but Maritz also bogeyed 16 to give Monasterio a one-shot cushion.
Monasterio hit a horrible approach into a greenside bunker at the closing hole at the Val Course at Aa Saint Omer Golf Club. He blasted out to 10 feet, then calmly holed the par save to get into the clubhouse at 10 under par, one shot better than Maritz.
Maritz only made par at the last and Nystrom birdied to tie for second place.
Monasterio anxiously waited for Maritz to play the last to see if the South African would force a playoff. When he did not, Monasterio began celebrating his new-found fortune.
'I knew that I had to wait for Martin to putt on the 18th before I knew that I had won, but I didn't think about the playoff,' admitted Monasterio. 'I kept the same confidence that I had since the start of the week, and always felt that I could win here. I like the course here, and was confident all week.
'This win is so important for my future, and I feel like this is the real beginning on The European Tour for me.'
Jean Hugo carded a 2-under 69 and tied for fourth place with Juan Parron, who posted a final-round, 3-under 68. The pair finished 72 holes at 8-under-par 276.
David Dixon (70) and Jamie Little (69) shared sixth at minus-7, while Paul Dwyer (69) and Pedro Linhart (68) tied for eighth place at 6-under-par 278.
Jesus Maria Arruti (69), Klas Eriksson (73), Mikko Ilonen (73), Raymond Russell (73) and Shaun P. Webster (74) finished in 10th place at 5-under- par 279.
Joakim Backstrom, who won this event last year, never mounted a serious defense of his title. He shot a 2-over-par 73 on Sunday and finished in a group tied for 53rd at plus-4.