It was the first opening day loss suffered by United since 1972.
Among the fiercest critics has been former Liverpool midfielder Steve McManaman - now working as a television pundit - who claimed that this is the weakest United squad in 20 years. The quality of the side was disparaged last term and that trend has continued into the reign of Louis van Gaal, who has been recruited as manager to turn the club's fortunes around.
Fletcher - who played the entire 90 minutes against Swansea - is convinced that his side will prove themselves before the campaign is over. "People have been waiting for an opportunity to have a go at United for years and this is the perfect time [to do it]," said the midfielder.
"It's a long season and I don't think they will be saying those things at the end of it. I believe we're going to have a very good season. All the players believe that too. Comments like [McManaman's] give us a greater determination, without a shadow of a doubt."