The second-seeded German, won also won the event 12 years ago, maintained his slim chance of qualifying for next month's ATP finals in London. The 35-year-old Haas already had become the oldest tournament winner of the season by winning in Munich in May.
"This victory is really something special," the 12th-ranked Haas said. "You don't win tournaments too often and this year I've won in my two favorite cities."
Haas, who improved to 15-12 in career finals, said he was proud of what he achieved after recovering from hip surgery in 2010.
"If you'd seen me 3½ years ago ... I was really asking myself if it made sense to continue," Haas said. "I have been paying a lot of attention to my fitness and nutrition and I am always looking to improve my tennis."
Haas came back from a break down to win the opening set and appeared in control when he broke Haase again and led 1-0, 40-15 in the second set. However, Haase won that game and broke Haas again at 5-4 when the 63rd-ranked Dutchman converted his first set point with a lob.
Haase had another break to go 4-2 up in the decider but immediately lost his serve on a double fault and failed to win another game. Haas closed out the victory on his first match point when Haase sent a backhand long.
"I am disappointed as I've had my chances," said Haase, who upset top-seeded Jo-Wilfried Tsonga in the semifinals. "When I broke him at 1-0 in the second set, I started to feel stronger. I believed I could turn around the match. But he played all or nothing at the end and that paid off for him."
It was Haase's second defeat in a final this year after a defeat three months ago in Gstaad, Switzerland. The Dutchman won both his career titles in Austria, on clay at Kitzbuehel in 2011 and last year.