A much changed United line-up had the perfect start with an early goal, but they failed to build on this and allowed Ajax to come from behind to snatch a victory with a late goal and ensure a nervy last few minutes for Sir Alex Ferguson.
Javier Hernandez opened the scoring after just five minutes stretching United`s aggregate lead to 3-0 but it was the visitor`s who looked the stronger taking advantage of some sloppy Red Devil`s play to dominate or long periods.
The home side did have opportunities to extend their lead but failed to take advantage and almost paid the price. In fact had David De Gea not made a fine save from a Siem de Jong header with the scores level the game could well have been taken to extra time.
The second period was all Ajax as United squandered possession allowing the visiting fans to give voice to their hopes but it was not until four minutes from time they were rewarded.
A free kick caught the United defence out and Toby Alderweireld headed powerfully home.
Substitute Danny Welbeck had earlier hit the woodwork but overall this was a game in which United`s fringe players failed to shine.
Referee: Damir Skomina (SLOV)
Venue: Old Trafford
Man Utd scorers: Hernandez 5
Ajax scorers: Ozbiliz 37, Alderweireld 86
TRIBAL ASKS: Do United have the strength in depth required ?
Yellow cards: Rafael (Manu), de Jong (AJ)