Hat-trick hero Robin van Persie scored two late goals to prevent newly-promoted Southampton ruining Sir Alex Ferguson’s 1,000th league match in charge as Manchester United manager.
The Dutch striker headed in Nani’s injury-time corner after levelling from close range to cap a dramatic recovery.
Southampton led through Rickie Lambert and Morgan Schneiderlin headers, either side of Van Persie’s first equaliser.
Van Persie also missed a 68th-minute penalty, when United trailed 2-1.
It was a heartbreaking finale for Nigel Adkins’ battling Southampton side who more than matched their illustrious visitors throughout a pulsating clash at St Mary’s.
Schneiderlin thought he had earned a famous victory for the South Coast club when he swooped on a slip from United defender Patrice Evra in the penalty area to plant a bullet header past Anders Lindegaard.
But ex-Arsenal striker Van Persie paid back a huge slice of his £24m transfer fee with his late rescue act.
He smashed in a rebound from Rio Ferdinand’s header for the second equaliser before sending a near-post header from Nani’s left-wing corner flashing across Kelvin Davis into the far corner of the net.