He was drafted by the New York Islanders as their first-round pick, #16 overall, in the 2004 NHL Entry Draft. He used to play for SaiPa in his native Finland.

 

Nokelainen came to North America in 2005 to play for Islanders. After 12 games with the club (he scored a goal and an assist), Petteri suffered a severe knee injury. Many thought that this injury would sideline him for the rest of the year, but the knee healed without surgery and Nokelainen had returned to finish the rest of the season with the Islanders, but his knee still needed healing and he got the surgery done. Thus ending his play for this season. On September 11, 2007, Nokelainen was traded to the Boston Bruins for Ben Walter and a conditional 2nd round draft pick.