Injury hit United earned a dramatic win at Watford through a late, late own goal from Troy Deeney just moments after the striker had pegged the Reds back in a thrilling finish at Vicarage Road.
Memphis had fired in a fine finish after 11 minutes to put Louis van Gaal's men ahead but-after a trio of spectacular second half saves from David De Gea- the Hornets pulled level with Deeney's 87th minute penalty to seemingly earn a deserved draw.
However, Deeney then turned Bastian Schweinsteiger's cross-shot into his own net to give us a precious victory and send United top of the league.
After recently including academy graduates Axel Tuanzebe and Cameron Borthwick-Jackson in his matchday squad, van Gaal named two more untested youth players on the bench in Sean Goss and Marcus Rashford.
It was another homegrown talent whom went close early on though, when Jesse Lingard narrowly failed to nod home Juan Mata's excellent cross with barely a minute played.
United were ahead soon afterwards however as former Watford man Ashley Young found Ander Herrera whom in turn picked out Memphis to crash home a brilliant first-time effort on the volley.
Odion Ighalo fired wastefully wide in the Hornets best opening of the half whilst Morgan Schneiderlin lashed narrowly over the bar at the other end.
Heurelho Gomes saved well from Memphis shortly before the break, but Watford soon took control and called De Gea in his first real action of the match.
Having saved well from Ighalo five yards out, the Spanish stopper then thwarted his strike partner Deeney before he tipped away a deflected effort from Almen Abdi as the Hornets continued to turn the screw.
Lingard had a chance to seal victory with a lob and that looked to be a crucial miss when Deeney slammed in the spot-kick after Marcos Rojo had tripped Ighalo.
United piled on the pressure in pursuit of a winner and, after Gomes saved superbly from Smalling, Schweinsteiger smashed across goal, the ball struck Deeney and trickled home as he attempted to clear to give the Reds a massively important win.
Overall team performance: 6.5/10
United Faithful Man of the Match: A tough call between Spanish Dave, Basti and Mike, but DDG edges it. Three top stops in the second half, one of which was world-class.