He may not be in the best form at the moment, but Van Persie has made a massive difference to Manchester United this season.
The Dutchman's goals in the first six months of the season set Sir Alex's men on their way to the title as they racked up crucial points.
Roberto Mancini made it clear that he wanted Van Persie at Manchester City this season, but United won the race for his signature.
How much difference would it have made if RVP was a City player? We will never know for sure, but there definitely wouldn't be a 15-point gap.
2. The African Cup of Nations.
City always knew the African Cup of Nations would leave them without Yaya and Kolo Toure for a few games and it could well have cost them crucial points.
In the four Premier League games these two missed, City started well with two victories, but then dropped points against Queens Park Rangers and Liverpool.
Yaya then came back in against Southampton, but he was perhaps tired from international duty and couldn't prevent a 3-1 defeat.
During a crucial spell of the season, this was a massively disappointing few weeks for City.
3. City's lack of goals away from home.
Last season, no team scored more away goals than Manchester City. They went to places with confidence and were clinical more often than not.
In the current campaign though, something is missing. During their 15 away games, they have scored just 20 goals - an average of just 1.3 per game. This is simply not good enough.
Relegation candidates Aston Villa can match this figure, while everyone else in the top seven have managed more goals on the road than City.
This has contributed to the reigning Champions dropping 19 points away from home.
4. United's consistency at home.
Manchester City's home form has been good - they have only lost once - but frustrating draws have cost them.
Mancini's men could only secure a point in home games against Arsenal, Everton and Liverpool. They led in two of these matches as well.
United have then lost once, but won every other Premier League game at Old Trafford.
City's best winning streak at home this season is four victories in succession, while United have won their last 12 home league games.
5. Sir Alex's hunger.
Make no mistake about it, when City won the title last season, Sir Alex Ferguson would have been desperate to get revenge this season.
This drive and hunger from the Scotsman has since rubbed off on the players, while City have faltered in a completely new position as they tried to defend a league title.
It has been on the pitch where United have won the league, but how they and their manager go about their business off it has definitely played its part.