The Manchester derby has always been a big deal in terms of city pride but now, after a gap of almost 40 years, it's a crunch match in the English Premier League title race, too.
United versus City in tonight's early kick-off pitches first against third and only five points separate the bitter rivals after United's surprise defeat at Wolves last weekend. City, meanwhile, made no mistake with a comfortable 3-0 home win over West Brom that set up the derby clash perfectly.
The good news for United last weekend was they could afford the slip-up without coming under great pressure. Although City won, second-placed Arsenal reduced the gap on United by only a point after allowing Newcastle to come back for that remarkable 4-4 draw.
United have just had their worst result of the season and yet still they lead by four points with 13 matches to play. Even if they lose tonight, they cannot be overtaken this weekend and they would be confident of rebuilding the comfort zone between themselves and the chasers over the coming weeks.
A plus for United is they lead the mini-league based on head-to-head results between the top five teams, which is so often an indicator of which team will finish as champions. They have played only four games in that category and accumulated eight points, whereas Arsenal have seven points from six games and City six points from five matches.
Significantly, when weighing up the match, United have won both home games in that category, 1-0 against Arsenal and 2-0 against Tottenham. They also have a perfect home record from their other games against top-half teams, which gives them a clear favourite's chance tonight.
It is also notable that United's last blank in a home league game was 14 months ago, when they lost 1-0 to Aston Villa. Their scoring run since has stretched to 24 games, of which they have won 22, and their commitment to attack at Old Trafford makes them hard to stop.
Early in that scoring run, on City's only previous visit to Old Trafford under Roberto Mancini, United won 3-1 in a League Cup semi-final second leg to knock out City. That was one of two galling games for City at Old Trafford last season in which United conjured a decisive goal in stoppage time.
Tonight could be a watershed moment for Mancini. For all his stylishness as a player, the City boss displays a stereotypically Italian mindset as a manager, whereby defeat is to be avoided at all costs and risk is to be eliminated. In previous away matches against the big five this season, at Arsenal and Tottenham, he has been content to play out goalless draws. The Manchester derby hosted by City in November also finished 0-0.
On another day, City could have nicked a 1-0 win in any of those games, which is the argument Mancini would use to justify his tactics. But last weekend's remarkable events showed that risk-taking is an important quality in the Premier League and teams that sit back, as Mancini likes City to do, usually get left behind.
Another sterile draw would not be a satisfactory result for City. That would leave the gap at five points, which is effectively six when factoring in United's superior goal difference (11 goals) and probably more in view of United's game in hand. City fans, if not Mancini himself, are likely to regret the manager's negativity if he does not seek to grasp this direct opportunity to strike a blow to United.
City have the weapons to hurt United. Carlos Tevez has been a goalscoring phenomenon since moving across town and the probing of David Silva and Adam Johnson might well open up the defence.
Betting on the goals in this match, as with the result betting, depends on whether you believe United will continue their scoring run or that City will stifle them. Often the best policy in this type of match-up is to back the better defensive team, but it is not as if United leave themselves open when they attack - they have kept a clean sheet in all four of their big-five clashes this season.
Backing City is unattractive, given Mancini's reluctance to press for a win, and United's win chance could be underestimated at the odds. If United win, over 2.5 goals looks likely as 22 of their 28 home wins since the start of last season have gone over that mark.
The other teams that rate well for a home win, not surprisingly, are Arsenal and Liverpool, who host Wolves and Wigan respectively. Both might come out on top on the handicap, although Liverpool backers are paying a premium now that Kenny Dalglish has got them back in the top six.
The aways that rate best are Chelsea, Aston Villa and Newcastle, although there are question marks against all three. Chelsea still aren't playing that well and hosts Fulham are solid; Newcastle face a resilient home team in Blackburn and Villa are plenty short enough for their visit to Blackpool.
Villa should win, as they are going well now and it was a boost that two of their players scored the goals in England's midweek win, but there is no value in the odds.
Shortlist: Manchester United, Doncaster, Hull, Sociedad, Mallorca, Roma, Cagliari, Millwall, Lazio, Montpellier, Genoa
TOP FIVE BETS
1 Doncaster home win
Visitors Portsmouth are winless in 10 and look beatable
2 Sociedad home win
In-and-out but have a perfect home record against bottom-half teams
3 Roma home win
Scoring is not a problem and home form remains strong
4 Montpellier away win
Slight risk in low-scoring league but look too good
5 Genoa away win
Hosts Bari are a team to take on almost every week