Will Keane grabbed a hat-trick as United's youngsters crushed FA Youth Cup holders Chelsea 4-0 on the night and 6-3 on aggregate.
Revelling in the atmosphere provided by over 9,000 fans, the Reds turned on the style after Ravel Morrison broke the deadlock with a deflected shot. After scoring twice from close range, Keane completed his treble after being brought down by Chelsea goalkeeper Jamal Blackman to the sound of 'Keano' booming around Old Trafford again.
Both sides took time to adapt to the surroundings with the pace and intensity slower than at Academy League level. The Reds started brighter with Will Keane charging down a Blackman clearance and Larnell Cole heavily involved on the right flank.
Gradually, Chelsea began to exert some pressure and United keeper Sam Johnstone pulled off a vital save to deny Milan Lalkovic following good work by Aziz Deen-Conteh. However, Morrison then started getting on the ball and showing off his range of tricks as the Reds' class came to the fore.
Michael Keane's overlapping run almost carved out a chance for Brother Will and Gyliano van Velzen was twice denied by blocks when shooting opportunites presented themselves.
Morrison glided forward to work Blackman for the first time and, seconds later, saw his deflected shot loop over the keeper for the opener after Paul Pogba cleverly touched off a van Velzen cross. Moments later and the aggregate lead belonged to United for the first time thanks to Will Keane's powerful far-post header following Sean McGinty's fine cross.
Chelsea tried to mount a second-half response but Johnstone pushed away a Lalkovic drive before the Slovakian volleyed over the bar. The hosts, driven on by the buccaneering Ryan Tunnicliffe, always remained a threat as the midfielder had three attempts on goal, two of which forced Blackman into saves.
And a third goal on the night arrived when Morrison timed his pass to substitute Tyler Blackett to perfection and the defender, playing left wing, crossed for Will Keane to bundle home from close range at the second attempt.
After a slow start, this became an exciting show from a young Reds team brimming with talent as the FA Youth Cup holders were humbled. There was a scare when referee David Webb inexplicably failed to award a foul on Johnstone by Daniel Pappoe but Lalkovic was unable to profit for Chelsea with the United goal gaping.
With time running out, another searing break by the stamina-packed Tunnicliffe allowed Will Keane to round Blackman, only to be fouled by the keeper's rash challenge. It merely delayed the centre-forward's treble as he steered the spot-kick into the corner of the net for 4-0.
The Reds still hungrily chased another goal to leave everybody thoroughly entertained and already eagerly anticipating the two-legged final with Sheffield United.