It is one thing overturning a 2-0 defeat in Europe when you are going well domestically, but it is another thing doing it off the back of a heavy defeat to Liverpool at home as United had to do.
The last time United pulled off such a feat off was 30 years ago when they beat a Diego Maradona-inspired Barcelona from a 2-0 first leg deficit, which underlines just how tough an ask this was.
The problem is that, just as at Celtic or Rangers, the manager of Manchester United is probably under greater scrutiny and media pressure than any other in his league.
But David was bold in his team selection and I thought his decision to restore Ryan Giggs, even at 40, was rewarded in spades, with a couple of the goals on Wednesday night.
The other thing that was unquestionable from the Olympiakos game was, that unlike some of the speculation of late, the players are still completely behind David.
Wayne Rooney's post- match quotes reflected that.
As a United fan you can now look at tomorrow's quarter-final draw with the likes of Real Madrid, Barcelona, Bayern Munich and, of course, Chelsea, and I'm sure a tingle of excitement will be running down their backs.