Haas picked up $52,000 in winning his first tournament title in over two years, his last victory coming at Stuttgart in October 2001.
The unseeded German missed all of last season with a shoulder injury and was playing just his fifth tournament of the year.
"To be honest, I didn't expect to win a tournament this quick but all you can do is prepare for each tournament and do your best and see what's possible," Haas said.
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Roddick has now lost all four career matches to Haas, although three of them came before the German's injury problems and before the 21-year-old Roddick emerged as one of the best players in the game.
The American was appearing in his fourth straight final here and has an 18-2 record at the event with both losses coming in title deciders.
Andre Agassi beat Roddick to win the 2003 title.
Roddick also had his overall winning streak stopped at 12 matches as Haas won his first clay court title.
