 Upon returning to Brisbane after the first round of trials, Tonelli tore rib cartilage while participating in judo at high school. The pain of the injury restricted him to swimming backstroke for four months, and his times steadily improved during this period under the guidance of John Rigby at the Valley Pool. At the final selection event, he came second in both the 100 m and 200 m backstroke behind Olympic gold medallist Brad Cooper to earn his international debut. At the World Championships in Belgrade, Yugoslavia, he came sixth in the 200 m backstroke behind East Germany's Roland Matthes, who set a world record. Tonelli self-deprecatingly noted that "I didn't get to see him [Matthes] swim in the final, because I was in the same race five sets of speedos behind".
