He made his CART debut in 1983, racing for the Kraco Enterprises team. Andretti re-signed for Kraco to undertake the 1984 season, where he managed five third-place finishes and ended his rookie season in seventh overall. In the Indianapolis 500, he finished fifth and shared the Rookie of the Year award with Roberto Guerrero. He went on to win his first IndyCar race in 1986 in the Toyota Grand Prix of Long Beach. The season became a two-man battle for the championship title, between Michael and Bobby Rahal. Andretti would take the points lead with his victory on the Milwaukee Mile. A week later, on Father's Day, Michael was leading on the final lap at Portland, when his March-Cosworth 86C ran out of fuel, allowing his father, Mario, to beat him by just 0.07 seconds. It was one of the most shocking finishes in the history of IndyCar, and the closest finish (until 1997). With Rahal continuing to win races, Andretti's consistent finishing only allowed Rahal a nine-point lead in the standing with two races remaining. Andretti won a key victory in at Phoenix. Going into the season finale at Tamiami Park, Andretti was just three points behind Rahal, but neither driver were a factor in the race, with Andretti retiring with a broken halfshaft.