Early career

On November 20, 1984, Zorko ran his first ever race, which he won on a cross country course at the age of 17.^[2] Less than a year into training, he posted a time of 8:30 for 3000 meters and won a competitive high school race called Kros Sportskih Novosti.^[2] He declined offers to train with AK Crvena Zvezda and instead remained in Križevci, where he did intervals on a track only once a week.^[2] The rest of his training took place on forest trails, where Zorko alleged that bystanders would ask him why he was running and tell him to "take a hoe and dig out some corn".^[2]

International

At his first major international competition, Zorko finished sixth in the men's 3000 metres race at the 1989 IAAF World Indoor Championships. In 1990, he won his first major medal, winning bronze at the European Indoor Championships in Glasgow. After the breakup of Yugoslavia, Zorko began specializing in middle-distance disciplines, and eventually found his talent in the 1500 metres. In 1992, Zorko won the first international medal for the newly independent Croatia, winning a bronze medal at the 1992 European Indoor Athletics Championships. A year later he won the bronze medal for the men's 1500 metres at the 1993 IAAF World Indoor Championships, finishing only 0.39 seconds behind winner Marcus O'Sullivan. Next year, Zorko finished second in the 1500 at the 1994 European Athletics Indoor Championships, and third at the 1994 European Championships in Athletics.

At the 1997 IAAF World Indoor Championships and at the 2002 European Indoor Athletics Championships, he finished in fourth place in the respective 1500 metre races.

Pacemaking

By the late 1990s, Zorko was increasingly suffering from injuries, which prompted him to turn to professional pacemaking. As a pacemaker, he assisted in setting several world records, both indoors and outdoors, most notably for Haile Gebrselassie. On July 11, 2005, Zorko announced his retirement at the IAAF Grand Prix Zagreb.

Outdoors

Indoors