Defensive stability cannot be overlooked. Granted, there is a lot more to winning a Premier League title than a team's centre-back pairing, but a successful partnership at the heart of any back line does provide one hell of an advantage.
What has proved vital to Manchester United this season, is the solidity of their side, which stems from the same central defenders that have been deployed, game, after game, after game.
Rio Ferdinand's partnership with Jonny Evans, in the absence of club captain Nemanja Vidic through a long-term knee injury, has been crucial.
In the last ten games, United have won nine and lost just once - the midweek slip-up against Wigan Athletic at the DW Stadium last Wednesday - the only blemish on the team's near impeccable record since the middle of February.
Sir Alex Ferguson's side returned to winning ways in yesterday's comfortable 4-0 victory over Aston Villa at Old Trafford - the club's sixth clean sheet in their last seven league outings.
With 27 points from a possible 30 pocketed during an important period in the race for the title, Ferdinand and Evans have played together in every single one of those games.
The contrast with Manchester City comes in the number of times first-choice pairing Vincent Kompany and Joleon Lescott, have been paired together - in only six of the last ten games.
Their results have been considerably worse, with six wins, two draws and two defeats, amounting to 20 of the 30 points on offer.
In short, that period is the reason behind the current five-point gap between themselves and Manchester United at the top of the Premier League table.
City have won five of the six games that Kompany and Lescott have played together, keeping four clean sheets, with the only defeat coming against Arsenal at the Emirates Stadium earlier this month.
The four games when the pair did not play together were hugely damaging for the club's title charge. From a possible 12 points, Roberto Mancini's men picked up just five, and losing seven points at this stage of the season, is huge.
Beneath City, Arsenal have undergone a mini-renaissance, hitting a golden period of form which matches United's run of nine victories from the last 10 games - where Thomas Vermaelen and Laurent Koscielny have played together on eight occasions.
The only difference here is that Vermaelen has started two of those games at left full-back, but the settled side - particularly in defence - that Arsene Wenger has been able to name in the past couple of months, has now dispelled the assertion that the Gunners are weak at the back, as they continue to go from strength to strength.
Meanwhile, for their north London rivals Tottenham, the picture appears a little more complicated, because Ledley King and Younes Kaboul - first-choice pairing in the absence of long-term absentee Michael Dawson - have played together in seven of the club's disastrous 10-game run that has yielded just 10 points for the Champions League hopefuls.
Having lost their stability, and their form, Spurs' recent slump is threatening to ruin their season, and their new-found defensive frailty was on show again in Sunday's FA Cup semi-final defeat against Chelsea, as Harry Redknapp's side were thrashed 5-1 at Wembley.
There's an old saying in football that success is built from the back, and in the case of having a water-tight defence - inspired by a strong centre-back partnership - that is true.
If coming together is a beginning, and keeping together is progress. Working together brings valuable reward, at the end of a long season.