London - Taking a break from their Premier League title race, the two Manchester clubs meet in the FA Cup on Sunday with United desperate to avenge a recent trouncing by City that signified to some a shifting of English football's balance of power.
City fans will have October 23, 2011, etched in their memory for years to come. That was the day the blue half of Manchester celebrated a 6-1 league victory at Old Trafford that underlined the team's emergence as a genuine force for the first time in a generation.
United have had to wait 11 weeks for payback, and will also be eager to exact revenge following a 1-0 loss to their neighbours in last season's FA Cup semi-finals at Wembley.
"The way we bounced back from the (6-1) was unbelievable," United defender Phil Jones said. "Not everyone thought we would. But that is what Manchester United does best - prove people wrong. When the chips are down, you see who the real fighters are."
United will need plenty of that fight if they are to come away from the Etihad Stadium with a victory or even a draw in what is undoubtedly the match of the third round, when the topflight teams enter the draw in world football's oldest knockout competition.
While United have lost their last two matches - to Blackburn and Newcastle - to slip three points behind City at the top of the Premier League, City's 3-0 win over Liverpool on Tuesday extended their perfect home record in the league to 10 matches this season.
City are also the FA Cup holders following the 1-0 victory over Stoke in the 2011 final that ended the club's 35-year trophy drought.
"We need to make sure we take this momentum (from the Liverpool win) because the games keep coming thick and fast," City midfielder James Milner said. "We had a couple of disappointing results over the Christmas period. We know it is a critical time over any season and ... it is a learning curve. We need to make sure we learn from those sort of experiences."
City manager Roberto Mancini will find out by Friday at the latest if Yaya Toure and his brother Kolo are available for the match before they head off to the African Cup of Nations with the Ivory Coast.
Gareth Barry is banned after his sending-off against Liverpool, fellow midfielder Owen Hargreaves - a former United player - is not considered fit enough to be involved and Italy striker Mario Balotelli has an ankle injury.
"We have 17 players," said Mancini, who said he may not be able to fill his substitutes' bench. "I do not know how it is going to work."
United's injury crisis is finally starting to clear up, with midfielder Anderson and defender Rio Ferdinand back as the team looks to bounce back from successive losses.
"It's not the time to panic. We have the patience and experience to cope with that," Ferguson said after the 3-0 loss at Newcastle on Wednesday.
Blackburn visit Newcastle on Saturday in the other all-Premier League match in the third round, which usually springs surprises as English football's smaller teams get a rare chance to stun mightier opponents.
Two non-league sides have advanced to this stage, with fifth-tier club Tamworth set to be cheered on by 4 300 of their fans when they travel from central England to play Premier League side Everton at Goodison Park on Saturday.
The romance of the FA Cup will also be seen at Highbury where Fleetwood Town, who are second in the fifth-tier Conference Premier, host Blackpool, who were relegated from the Premier League at the end of last season.
Arsenal will hope to have clinched the loan signing of former striker Thierry Henry in time for their home match against Leeds on Monday and Chelsea host second-tier club Portsmouth in a repeat of the 2010 final, which the London club won 1-0.
Tottenham, who are third in the Premier League, host League Two team Cheltenham while seven-time winner Liverpool kick off the third round with a home match against fellow northwest team Oldham on Friday.