Victory over the Dutchman took two and a quarter hours and denied Haase his third trophy in Austria after twice winning on clay at Kitzbuehel.
Haas first won in Vienna in 2001 having lost the final the year before to Tim Henman.
"Winning a title doesn't come around that often, so it's a great feeling having done it twice this year," said Haas, the father of a young daughter whom he said is one of the main motivations keeping him out on court at the age of 35.
"It's a great feeling to have done it here again," added the son of an Austrian father who lived for nine months as a child in Vienna. "This is really a special place for me, it's all a great feeling for sure."
Haas, who also won Munich on clay in the spring, stayed in the race for one of the four spots remaining in the eight-man World Tour Finals starting in a fortnight in London.
He currently stands provisional 12th.
"I still have a small chance, but I have to play extremely well," Haas said of the slim possibility of earning a place in the season wrap-up for the first time.
He will try to push his case over the final two weeks of the regular season in Valencia next week followed by the Paris Masters.
"It may mean that I have to win Paris," he said. "I have to give my best tennis, nothing is impossible. I want to play good tennis for the rest of the season."
Haas, with 15 career titles from his 27 finals, hit back after going down an early break in the first set against Haase, with the German winning six of the next seven games to claim the set and begin the second with a break of serve.
Haase broke back and eventually squared the final at one set each on a lob winner.
In the deciding set, Haas broke for 5-4 and took victory a game later on his opponent's long forehand.
"It was back and forth at the start," said Haas. "It was a final and we were both perhaps a bit nervous.
"I got a better groove going and moved up a set and a break but I played some loose errors and he got back in the match.
"He took the initiative and I didn't feel like I was playing my best tennis, I changed racquets to try and get a bit more firepower and won the next four games. It was good enough to win today even if I was not playing my best."
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