Whoever does come through will start as favourites to win the FA Cup itself on May 14 when they will face the winners of Sunday's other semi-final between Bolton Wanderers and Stoke City.
For different reasons both matches have excited the imagination of fans beyond just the teams involved - Saturday's because of the intense rivalry and significance of the tie to both Manchester clubs, and Sunday's because Bolton and Stoke rarely come so close to glory.
United have won their last seven matches in all competitions and are on a high after beating Chelsea 2-1 on Tuesday for a 3-1 aggregate success to secure a place in the semi-finals of the Champions League.
United are also seven points clear of Arsenal at the top of the Premier League and there is a possibility they could repeat their Champions League, Premier League and FA Cup treble of 1999 as they have hit form at just the right time.
Although they will be without the suspended Wayne Rooney, Ryan Giggs, 37, has been outstanding in their recent run of victories.
"Our confidence is really high and players are coming back from injury and that's what you want at this stage of the season as there are games every three days," said Giggs.
"The manager will chop and change the team... but we've got 20 players probably competing for 11 places."
Unfortunately for United, Rooney, who has returned to form with 10 goals since February 1, is unavailable following his swearing incident at West Ham United two weeks ago.
City may also have to make do without the services of former United striker Carlos Tevez, who picked up a hamstring injury on Monday.
His absence could dent their chances of reaching the final for the first time since 1981. Thirty years ago they lost 3-2 to Tottenham Hotspur in a replay while their last FA Cup success was in 1969 when they beat Leicester City.
Although owner Sheikh Mansour has invested hundreds of millions into the club, City have yet to end their 35-year wait for a major trophy and will have to show a dramatic improvement on their abject display in Monday's 3-0 loss at Liverpool to prevent United rubbing their noses in the dirt again.
EVEN LONGER
While City's wait for major honours has lasted since 1976 when they won the League Cup, Bolton and Stoke have gone even longer without collecting a major piece of silverware.
Stoke, who have been playing in the FA Cup since 1883, have never reached the final. They last reached the semis in 1972 when they lost to Arsenal. That was also the year they won their only major trophy beating Chelsea in the League Cup final.
Bolton have won the FA Cup four times, the last of those triumphs coming in 1958 when Nat Lofthouse, their greatest ever player who died earlier this year, scored both goals when they beat Manchester United 2-0 at Wembley.
Both sides, sitting comfortably in mid-table, have beaten each other in the Premier League this season, and Bolton manager Owen Coyle says th
