"I was dreaming my whole life to win a title," said the 23-year old Spaniard. "It's a great win and I think this will give me confidence to go up in the rankings and be a great player."
Canas, who was also beaten in the 2001 final, was seeking his fourth title of the year following victories in Stuttgart, Umag and Shanghai.
Having begun the year ranked 274 after playing just five events in 2003 and undergoing double wrist surgery, Canas has climbed to 26th in the world.
However, the Argentine was unable to continue his winning form against an enterprising opponent.
Eighth seeded Lopez, who was beaten by Roger Federer in his first career final in Dubai earlier this year, took three hours 35 minutes to earn victory.
The Spaniard earned the decisive break for a 6-5 lead in the final set when Canas struck his eighth double fault.
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Lopez had beaten Canas 10-8 in the fifth set in their only previous encounter, at Wimbledon two years ago, and was once again the more adventurous player.
Canas's nerves also failed him as on several occasions he double-faulted on break points, allowing Lopez to gain advantage in the first set.
The Argentine reduced his errors in the second set and dropped just two points on serve but Lopez took the third by breaking in the final game when Canas made a backhand error.
Canas appeared to be gaining the upper hand, winning the last four games of the fourth set as Lopez began to tire.
However, Lopez hung on in the third before earning the vital break in the decider.
"It's an unbelievable feeling." said Lopez.
"It was a very close match. Guillermo was playing unbelievable, fighting for every ball. You have to win the point four or five times.
"At the beginning of the fifth set I wasn't sure I could get the title because he was playing good the whole time and I was tired a little bit but I got the break and finally I won."
Canas said he paid the price for his inconsistent form.
"I didn't have my best day. I was up and down in my level, but he was serving well and he played very well," said Canas.
