 Mäntylä came through the youth ranks of Tampere Tappara and made his debut in Finland's top-tier Liiga in the course of the 1999–2000 season.He won the Finnish national championship with Tappara in 2003 and subsequently parted ways with the team to take his game to Sweden, where he joined Luleå HF of the Swedish Elite League (SHL).He enjoyed a two-year stint there, before returning to Tappara.