Seles, a former World No. 1, moved within three tournament victories of Britain's Virginia Wade for seventh place on the WTA list of most career titles in the Open era (since 1968).
The 28-year-old earned the $27,000 winner's check and captured her first title in 2002. Seles finished last year with a flourish by capturing three straight WTA crowns.She won at the Brasil Open in September and the Japan Open and Kiwi Open in October.
"It was a hard fought match and the conditions were very tough as it was very windy," Seles said. "Tammy played very well and she brought (out) the best in me. I was lucky enough to win the first set."
Seles won this event in her debut at Doha. She had reached the final of the Pan Pacific Open at Tokyo and the last four at the Australian Open and the Open Gaz de France in her previous three outings in 2002.
"I had some chances to break and she had some chances too," Seles said. "I struggled with my forehand, it was one of those days."
Tanasugarn, 24, failed in a bid to win her first career title. She lost to Anna Smashnova in the final at Canberra earlier this year. Tanasugarn entered this tournament a career high ranking of No. 21 and reached the third round at the Australian Open last month.
"I am very happy with the way I played today, even though I did not win. Monica is very tough to play against," Tanasugarn said. "I had some chances but did not take them."