At age seven Mandich learned to skate and by 10 he was playing with the Nadrofsky Steelers. It was the first Brantford team to win the All-Ontario Championship. At 17 he began playing with the Windsor Spitfires, but was injured during the season and finished the year with the Windsor Royals, winning the Southwestern Ontario Championship and all Ontario runner-up. The next year Mandich received a scholarship to play at Ohio State University, where he was selected as the Central Collegiate Hockey Association First Team All-Star and Ohio States All-Century team. Between 1982 and 1986 he played with the Minnesota North Stars until a career ending injury.