Puninski competed for Croatia in the men's 100 m butterfly at the 2008 Summer Olympics in Beijing. Leading up to the Games, he finished with a third-place time in 52.61 to dip beneath the FINA A-standard (52.86) by 0.25 of a second and earn a direct Olympic selection to the Croatian squad at the USA Swimming Grand Prix in Columbus, Ohio. Coming from third at the halfway turn on the outside in heat six, Puninski faded down the stretch to hit the wall in dead-last with a 53.65. Puninski failed to advance into the semifinals, as he placed forty-seventh overall out of sixty-six swimmers in the prelims.