18 year old striker Marcus Rashford enjoyed a night to remember as he marked his debut with a brace of goals to help fire United into the last 16 of the Europa League.
The Reds overturned Midtjylland's first leg advantage despite falling behind at Old Trafford to advance with an eventual stylish and comfortable victory.
Pione Sisto, whom scored in the first match, followed that up with the opener here to leave United needing three, but Nikolay Bodurov's own goal, Rashford's brace, a Herrera penalty and a scintillating strike from the outstanding Memphis ended the resistance of the tiring, ten man visitors.
Anthony Martial was injured in the warm up, with Rashford promoted from the bench to cover for the Frenchman and the Wythenshawe Academy graduate was soon in the thick of the action.
The forward had a low effort well saved by Mikkel Andersen, Kris Hansen almost deflected a Memphis cross into his own net and Kristoffer Olsson's shot cannoned off Jesse Lingard and wide as the visitors rode their luck.
Out of nothing, though, the Danish side sent Old Trafford into stunned silence as they took a
3-1 aggregate lead on 27 minutes through Pisto, whom dribbled through the defence and slotted in a neat finish.
United were level on the night only five minutes later as Juan Mata and Guillermo Varela linked up to play in Memphis, whose dangerous cross was turned past Andersen by Bodurov.
Morgan Schneiderlin struck the post with a header from debutant Joe Riley's cross before United were awarded a penalty for a foul on Herrera by Andre Romer.
Juan Mata stepped up but saw his weak spot kick palmed out by Andersen with two first half minutes remaining.
Schneiderlin and Herrera both squandered excellent chances but Midtjylland were finally undone when Mata found Rashford to pounce from close range and level the aggregate score at 3-3 just past the hour mark.
At that stage, the tie was heading for extra-time but the Reds relentlessly continued to press and moved ahead overall with 15 minutes to play.
Things got even better for the youngster as he found himself in the right place at the right time to convert Varela's excellent cross before he headed narrowly over as he chased his hat-trick.
Herrera smashed home the fourth from the spot after Hansen's handball, and Romer was then sent off for a second booking having tugged back Memphis.
The winger - a thorn in the Midtjylland side all game - got the goal his excellent performance deserved when he arrowed in a sweetly struck drive after a teasing run from deep.
Sub Andreas Pereira went close to a sixth, Marcos Rojo returned from injury and Regan Poole made his debut as this was a job well done by the Reds to move into Friday's draw.
Overall team performance: 8/10
United Faithful man of the match: Memphis had his best game in a United shirt. More of the same please...