Federer improved his 2004 match record to 15-1 with a 7-6 (9-7), 6-2 win over his Finish opponent. Federer has won all five career meetings with Nieminen and has yet to lose a set.
The only seeded player to reach the semifinals, Federer is making his first appearance since his 16-match winning streak was stopped in the Rotterdam quarterfinals two weeks ago.
Federer can become the first back-to-back winner of this event when he plays Feliciano Lopez of Spain in Sunday's final.
Lopez defeated Mikhail Youzhny of Russia, 6-4, 4-6, 6-4 in the other semifinal. Lopez advanced to his first ATP final after losing in the opening round of his previous three events this year.