When Scott Laird fired the League One side ahead minutes into the second half it looked like United would go out of a cup competition to a League 1 side for the second time this season.
But Louis van Gaal yanked off the disappointing Radamel Falcao and suddenly United’s attack had purpose and fluidity, with recalled midfielder Ander Herrera pulling the strings from nmidfield.
Herrera started for only the third time in the last three months, a stat that baffles United fans as he has looked impressive whenever he has been on the pitch. It was Herrera, just like he did at Yeovil in the last round, who scored, before Marouane Fellaini’s close-range finish gave United the lead in a thrilling tie.
Rooney, back playing in a more advanced role, made certain of victory with a late penalty that he won and converted himself to give the scoreline a gloss that Preston did not deserve.
With Rooney playing higher up the pitch from the deeper midfield position he has occupied recently, the United captain put in one of his best performances in weeks.
Angel Di Maria bent a free-kick a few inches wide but that was the closest the 11-times winners came to making the breakthrough before the interval.
However you described Van Gaal’s latest formation – 4-1-2-2-1 being a close approximation – it was not helping United turn their vastly superior possession into chances.
When they did find time and space in dangerous positions their delivery was frequently disappointing, with Di Maria a repeat offender with wasted balls.
It all meant Preston goalkeeper Thorsten Stuckmann did not have a shot to save before the break
North End’s own threat had been restricted to a couple of tame shots from distance and a Joe Garner header that looped over the bar.
But that all changed two minutes into the second half when Garner sent Laird galloping into the box to power in a shot that was heading wide before deflecting off Antonio Valencia and squeezing under De Gea.