Coach Paulo Bento made eight changes to the side that started Saturday's 1-1 draw against Chile but his players gelled quickly and went ahead on 10 minutes with midfielder Micael sliding to toe-poke a Ricardo Quaresma cross into Otto Fredrikson's net.
The Finns were timid going forward and only came close to equalising in the 33rd minute when Daniel Sjolund sent a volley over Eduardo's bar after a fine pass by Roman Eremenko.
With Ronaldo sidelined by a hamstring injury, Quaresma and Danny took the opportunity to shine on the wings but their crosses were met by wasteful finishing by their team-mates, particularly striker Hugo Almeida.
Nani came off the bench on 68 minutes and made a difference almost instantly, winning a ball in the Finnish half two minutes later and squaring it for the unmarked Micael to score his second with the easiest of tap-ins.
Portugal are second in Euro 2012 qualifying Group H, three points adrift of leaders Norway, with the two sides due to meet in Lisbon on June 4. The Finns are fifth in Group E.
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