The top-seeded Monfils rallied for a 7-5, 3-6, 6-2 victory in a little under two hours. He captured his first title of the season and fourth of his career, though was also appearing in his 15th ATP final.
The Frenchman earned the victory Sunday thanks to a strong service game. He fired 13 aces and got his first serve in play 72 percent of the time, while winning 70 percent of those points.
He used the performance to win his first title since last October in Montpellier. Monfils had lost two finals since them -- to Robin Soderling in Paris last November, and to Radek Stepanek at the U.S. Open tuneup in Washington, DC this summer.
Nieminen fell to 1-10 in ATP finals, and became a runner-up at this event for the third time. He lost to Dutchman Sjeng Schalken in 2001 and James Blake in 2006.
Monfils, who collected $135,000 for the victory, improved to 2-0 against Nieminen. He beat the 73rd-ranked Finn in their first career meeting just three weeks ago in the Bangkok quarterfinals.