The 35-year-old lifted his first ATP Tour crown of the season and his fourth on home soil after a comfortable 6-3 7-6 (7/3) win over his compatriot.
"It's a sensational feeling to be quite honest," said Haas, who will rise to the 13th in the world rankings, on the ATP official website.
"It was another one of those milestones that I hoped for, to maybe win this title one year. To have done that, this late in my career, is a big highlight for me.
"Every time you win a title, it's a reflection of putting everything together the whole week. It doesn't happen that often. You're really proud of those moments."
Haas, who was ranked as high as number two in the world in 2002, has already beaten Novak Djokovic this year and this week's success proves he is still capable of causing an upset during the clay court season.
He did have to hold off a late surge from Kohlschreiber, who broke Haas in the 10th game to level proceedings in the second set when the veteran had the chance to serve for the match.
However, Haas rallied strongly in the tiebreak and claimed victory at the second attempt to deny Kohlschreiber the chance to win this tournament for a third time, following success in 2007 as well as last year.
"I knew it was going to be tough," added Haas.
"He's played well here before and was looking for his third crown and it was maybe my last opportunity to win the title here.
"So I gave myself a little bit of extra pressure. I served well and I played well when it counted.
"When I was serving for the match, he played aggressive, came up with some good shots, and was rewarded for it. Then I told myself to get into the tie-break and play it as well as you can.
"I didn't want to play a third set against him, having served for the match, so I was really pleased with that."
Kohlschreiber preferred to focus on the positives despite Sunday's setback.
"It's very frustrating to lose in the final, of course, but Tommy played a very good match," said the 29-year-old.
"It was a great week; it's always special to play at home. I'm happy with my performance. I really look forward to the upcoming clay-court tournaments.
"I'm pretty confident playing on clay and hopefully I'll have a good run."