United's biggest underdog story in a cup final?

Only the most blinded and/or loyal fan gives us a prayer in the FA Cup final. After watching the speed and technical quality of the game last night, this has only been exacerbated, especially so when compared to our brand of football and form since winning the league cup.

We've been underdogs going into finals before, but has it ever been to this degree where barely anyone believes we have anything more than a puncher's chance, or that it's a matter of how many we lose by and how badly we'll be toyed with?
Our CL Final with Barcelona in 2011, I guess.
 
I think the issue is that this seems to be the worst of us and best of them. Martinez and Varane are the spine of this team along with Bruno, Casemiero and Rashford. Two are out and two are out of form with Bruno still doing fine. So it’s not like (as of now) it’s City vs post WC confident United.
 
We were lucky to not concede more against Spurs, Brighton West ham. We can´t score a goal to save our lives at the moment.
Could see us pull off a miracle here with City not having their best game in front of goal. Maybe Rashford can get on a lucky break and score.
The fact we need a miracle here is a bit sad.
 
In many respects yes, especially since Liverpool were going for the treble of League, FA cup and European cup. However, Liverpool had 'only' won their second league on the trot, and had not achieved their decade of dominance. United were close to them the season before. Make no mistake Liverpool were the favourites, but the FA cup had thrown up so many surprises in the 1970s, not least second division Southampton beating United the year before (which was largely seen as a done deal by United fans in my recollection), and Sunderland's totally unexpected victory over dominant Leeds in 1973. Even though the big teams have dominated post-millennium, there have still been some surprises such as Wigan and Leicester.

I think most MU fans are pessimistic based on current form, including me, but it was not that long ago United beat City and Barcelona. It is possible; unlikely but possible. And just maybe history will repeat itself and we will once again be treble party poopers, and I for one will 'love it' if we beat them.
Great post and yeah football on general was a lot more unpredictable back then before the gap between the top and bottom teams started to widen post bosman (although it was mostly a gradual thing obviously) but with hindsight I think it's fair to say that that Liverpool side reached greater heights than what city have even if they complete their treble so it's a tough call either way.