Mike Dean awarded what looked a blatant penalty after having a fine view of the incident but van Persie was guilty of over-elaborating from the spot and Davis atoned for his mistake by pulling off a comfortable save. It appeared to be a serious blow to any hopes of overturning the deficit and the Reds seemed stunned for some time afterwards.
Substitute Javier Hernandez wriggled free to force a desperate last-ditch tackle by Clyne before the late drama unfolded - just when hope seemed to be lost with only three minutes left. Rafael's cross was headed against an upright by Ferdinand but van Persie pounced on the rebound to lash into an unguarded net. In stoppage time, he completed the rescue act with a bullet header from Nani's inviting corner to spark scenes of jubilation in the away end, jacknifing a wonderful finish over Davis.
It looked like being the most frustrating of afternoons, but instead became a glorious, memorable occasion with van Persie well on his way to becoming an Old Trafford hero.
That is what supporting Manchester United under Sir Alex has been all about and, for all the excitement of the past, few of the 1,000 games will match this one for raising the blood pressure and the sense of euphoria will last all the way until the next league outing against Wigan in 13 days' time.