Kunitz was originally signed as an undrafted free agent by the Mighty Ducks of Anaheim on April 1, 2003. He split his professional rookie season between Anaheim and their American Hockey League (AHL) affiliate, the Cincinnati Mighty Ducks. After spending the 2004–05 NHL lock-out with Cincinnati, he was picked up on waivers by the Atlanta Thrashers in 2005–06. Two weeks later, however, he was re-claimed off waivers by the Ducks and went on to play 67 games with them, scoring 19 goals and adding 22 assists for 41 points, surpassing Paul Kariya's club record 39-point rookie season in 1994–95 (Kunitz still qualified as a first-year player because he did not play the minimum required games with Anaheim in 2003–04 to register as his NHL rookie season; the record was broken the following season by Dustin Penner's 45 points).