Arsenal arrived at a baking hot Wembley in May 1979 determined to make amends for their shock defeat at the hands of Ipswich Town a year earlier.
Terry Neill's side had been off colour against Bobby Robson's underdogs but they would not be denied for a second season in succession. However, few would have predicted the nature of their victory.
Bailey misjudged the cross and Sunderland raced in at the far post to slide in the winner. His celebration remains one of the FA Cup's iconic moments and no wonder.
With Liam Brady pulling the strings in midfield, Arsenal took a firm grip on proceedings and led by two goals at the break. Brian Talbot was credited with Arsenal's first although Alan Sunderland almost beat him in a race to apply the finishing touch. Then Brady glided down the right and crossed for Frank Stapleton to nod firmly past Gary Bailey.
That seemed to be that. The Final was petering out towards a comfortable Arsenal victory but, with five minutes left, the drama began. Gordon McQueen started it off, turning in a low cross to throw United a lifeline. Then Sammy McIlroy jinked past two challenges and poked the ball past Pat Jennings as the Arsenal keeper rushed out.
United were buoyant; Arsenal were stunned. For so long Neill's men looked certain victors, now the momentum was firmly with their opponents. But there would be one final twist in this incredible Cup Final.
Brady picked up possession from the kick off and, determined to keep the ball away from danger, surged into the United half before pushing the ball out left to Graham Rix. The placement of Brady's pass forced Rix to attack the ball and swing in a first-time cross. It was a beauty.
Bailey misjudged the cross and Sunderland raced in at the far post to slide in the winner. His celebration remains one of the FA Cup's iconic moments and no wonder. Arsenal had wobbled horribly but recovered in the nick of time. The Cup was heading back to Highbury.
This information has been verified by Arsenal's Club Historian