Most believe the answer here is based in Super Bowl III, widely known as the greatest NFL upset of all-time. And with their 16-7 win SU against an 18-point spread, the New York Jets became – and have remained – the biggest underdog to win ATS in the Super Bowl.
The biggest Super Bowl favorites to date, however, were the San Francisco 49ers of Super Bowl XXIX. Going in as 19-point favorites, the 49ers made apparent that they’d be covering the 19-point spread easily, and won the game SU over the San Diego Chargers, 49-26.