The eliminations of Chelsea, Manchester City, Tottenham Hotspur and Southampton have cleared the route for United and Arsenal, and it is an opportunity that both teams are desperate not to squander.
Recent events have left the FA Cup as the last realistic opportunity for both sides to apply a silver sheen to seasons that are rolling towards uncertain conclusions.
The pair remain well placed to qualify for next season's Champions League, with Arsenal currently third in the Premier League table and United a point back in fourth.
But Arsenal are on the brink of elimination from this season's Champions League after a 3-1 first-leg loss to Monaco in the last 16, while doubts continue to dog United as they struggle for form under Louis van Gaal.
Arsenal have won four matches in a row in the league, but recent history has given them reason to fear trips to Old Trafford.
Arsene Wenger's side have not won there since September 2006 -- a run of 10 matches that includes two FA Cup defeats and a scarring 8-2 annihilation in the league in August 2011.
The Arsenal manager refuses to entertain talk of bad omens, however, saying: "I don't believe too much in history
I just believe in the performance on the day
At the moment we are doing very well away from home.
"The size of the pitch is exactly the same everywhere
It is just down to how much we turn up and how much effort we put in to win the game
Both teams will think, 'If we get over this hurdle, we have a good opportunity to win the competition.'
"We are confident from our Premier League run, so we go to Manchester United to qualify and to give absolutely everything."
- United's 11-year itch -
With 11 titles each, United and Arsenal are the two most successful teams in the history of the FA Cup.
Their 14 previous encounters have yielded some of the competition's most enduring moments, from Alan Sunderland's late winner for Arsenal in 1979's 'Five-minute Final' to Ryan Giggs's sensational solo goal to settle the tournament's last ever semi-final replay in 1999.
Arsenal endured a trophy drought of nine years between beating United on penalties in the 2005 final in Cardiff and coming from behind to beat Hull City 3-2 at Wembley last May.
But it is even longer -- 11 years -- since United last lifted the trophy and captain Wayne Rooney is far from alone in Van Gaal's squad in having an FA Cup-shaped hole in his collection of winners' medals.
"We haven't been to a final for a few years
We want to try to win that game and we are looking forward to that," said the England striker.
"Of course, I think it is a massive trophy
It is a trophy that, growing up as a youngster, I used to love watching and I was fortunate enough to see Everton lift the FA Cup in 1995 when I was nine years old.
"It is something which I would love to do and hopefully it can be this year."
Robin van Persie and Juan Mata are the only members of the United squad to have won the FA Cup, but Van Persie's success came with Arsenal in that 2005 final and Mata's was with Chelsea in 2012.
An ankle injury means that Van Persie will miss the reunion with his former club, while centre-back Jonny Evans begins a six-match ban for spitting at Papiss Cisse during United's 1-0 win at Newcastle United on Wednesday.
Arsenal centre-back Gabriel has been ruled out with a hamstring injury, while goalkeeper Wojciech Szczesny (illness), defender Nacho Monreal (back) and midfielder Mathieu Flamini (hamstring) face fitness tests.
Source : AFP
Source: AFP