The season began ominously for the Colts when they were defeated at home on opening day by the St. Louis Cardinals and their journeyman quarterback, Tim Van Galder. In week two, Johnny Unitas threw for 376 yards and three touchdowns, but it was far from enough as Joe Namath threw for 496 yards and six touchdowns to power the New York Jets to a 44–34 victory at Memorial Stadium, the Jets' first victory over the Colts since Super Bowl III.
In October, the Colts' season reached its nadir when it was shut out twice at home in a three-week stretch by the Dallas Cowboys, who undoubtedly wanted revenge for their loss to Baltimore in Super Bowl V, and the Miami Dolphins, who were on their way to a 17–0 season and their first Super Bowl championship under former Colts coach Don Shula.
Unitas made his final start in a Colts uniform in a week 12 victory over Buffalo.
For the third consecutive campaign, the Colts played their season finale in Miami's Orange Bowl. Only this time, it was a humbling 16-0 shutout to the Dolphins in Week 14 in a game which was nowhere near as close as the final score. Baltimore ended its 1970 season by defeating the Cowboys in Super Bowl V, and its 1971 season by losing to the Dolphins for the AFC Championship.