The Finnish star reached the milestone 34 seconds into the second period when he scored into an open net after taking a feed from defenseman Scott Niedermayer during a power play. Colorado netminder Craig Anderson was caught out of position on the play following a scramble in front of the crease.
Selanne's historic marker gave the Ducks a 3-0 lead and proved to be the decisive tally. With the goal, Selanne became the 18th NHL player and the third European to score 600, including fellow Finn Jari Kurri (601) and Czech Jaromir Jagr (646).
The Ducks also got goals from Ryan Getzlaf, Jason Blake, Matt Beleskey and Troy Bodie in the victory, while Jonas Hiller made 26 saves.
The Avalanche got goals from Darcy Tucker and Ruslan Salei in the defeat.
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