Andretti made his Champ Car debut on April 19, 1964 at the New Jersey State fairgrounds in Trenton, New Jersey. He started sixteenth and finished eleventh. Andretti was introduced by his USAC sprint car owner, Rufus Gray, to veteran mechanic Clint Brawner. Brawner was not impressed since sprint car drivers Stan Bowman and Donnie Davis had recently died, and Brawner's current driver, Chuck Hulse, had been critically injured. Chris Economaki recommended Andretti to Brawner, so Brawner watched Andretti race at Terre Haute, Indiana. Brawner was convinced that he had found the new driver for his team. The two stayed together for six years. Andretti finished eleventh in the USAC National Championship that season. Andretti won his first championship car race at the Hoosier Grand Prix on a road course at Indianapolis Raceway Park in 1965. His third-place finish at the 1965 Indianapolis 500 in the Brawner Hawk (a mechanical copy of the current Brabham Formula 1 design) earned him the race's Rookie of the Year award, and contributed towards Andretti winning the series championship. He was the youngest national champion in series history at age 25. He repeated as series champion in 1966, winning eight of fifteen events. He also won the pole at the 1966 Indianapolis 500. Andretti finished second in the IndyCars in 1967 and 1968. He also won a single non-championship drag race in 1967 in a Ford Mustang. In both 1967 and 1968, Andretti lost the season USAC championship to A. J. Foyt and Bobby Unser, respectively, in the waning laps of the last race of the season at Riverside, California—each by the smallest points margin in history.