Thursday night in Europe's second tier competition must have been a weird sight for United supporters and early on it appeared that their team would just go through the motions with a big win over the Dutch champions expected.
Frank De Boer's Ajax were the more dangerous of the two sides in the first half but soon enough Sir Alex Ferguson had his Red Devils up and about and they came away with a handy advantage heading into the return leg next week.
After an initial 45 minutes of little creativity, United sprung into gear in the second term and finally made a breakthrough when Ashley Young slotted through the legs of goalkeeper Kenneth Vermeer just before the hour-mark. The goal came about when Nani's cross from the right deflected to Young who took three touches to get around his marker before finishing neatly to give the visitors the ascendency.
The Red Devils picked up their game dramatically as the game progressed and gave themselves a two-goal buffer with just over five minutes remaining when Wayne Roonye played a neat through ball for Javier Hernandez who managed to finish calmly despite the best efforts of Ajax keeper Vermeer.
United keeper David de Gea was called on a few times throughout the 90 minutes, particularly when Siem de Jong hit a very dangerous shot from outside the area which was headed for the Spaniard's top left corner but he was able to pull off a vital save.
Of the two keepers, Vermeer had more work to do in the end and he had to be at his best to keep out Nani's audacious effort early in the second half before Rooney's deflected header caused a few problems but the 26-year old was up to the task.
All in all, however, it was a good enough performance from United to give themselves every chance of progressing to the next phase with a two-goal lead heading into the Old Trafford leg.
UEFA Europa League Round of 32 - first leg
Amsterdam Arena, Amsterdam