Monaco, the No. 3 seed, ended the run of qualifier Guido Pella with a 6-4, 7-6 (10-8) victory. Pella had beaten No. 1-seeed Janko Tipsarevic and seventh-seeded Viktor Troicki, to get to the semifinals.
Monaco didn't face a break point in taking the first set but had lost his serve twice in the second set to force the tiebreaker.
Nieminen, seeded sixth, got by Igor Sijsling 7-5, 4-6, 6-3. He had three breaks in the first set and two more in the third.
Nieminen has won two of the three times he's played Monaco but they haven't met on the court since 2010.
Nieminen is just 2-10 in ATP finals. He won the Apia International in Sydney in January 2012 in his most recent finals appearance.
Monaco is 7-9 in championship matches after winning four of his last five finals appearances. He won in Malaysia in September, in his last previous title match.