, but this time from City back to United.
Alex Ferguson owes Arsene Wenger a thank-you card because his Manchester United team would not be at the top of the league if the Arsenal manager hadn't sold him Van Persie.
What a bargain Ferguson struck in getting the Netherlands striker for a reported $38 million. For United fans, Van Persie's match-winning goal on Sunday alone was priceless because of the dagger it plunged into the heart of rival Manchester City.
In four months since he walked out on Arsenal to move to the city in England's northwest that is becoming the epicenter of English soccer, this was already the fifth time that Van Persie has scored the winning goal in a league game for United. Even Ferguson cannot have imagined that Van Persie would have such an immediate and decisive impact when he signed him in August.
Van Persie got the hat trick at Southampton in September when the Reds were just four minutes from defeat in Ferguson's 1,000th league match as United manager.
He scored a late penalty kick three weeks later that made it 2-1 for United at Liverpool and a goal after just 32 seconds at Old Trafford that defeated West Ham in November.
Van Persie also scored the winner in United's 4-3 defeat of Reading and now, the following weekend, the left-footed free kick in injury time that made it United 3, City 2.
That's now 11 league goals for Van Persie in United red.
Even more important for his team is that his goals are earning vital points from matches that seemed likely to deliver just one point or none to the Reds. Sunday's game was heading for a draw before Van Persie secured all three points for United in the 91st minute.
Van Persie could now argue that his outright winners and other goals that contributed to defeats of Fulham, Chelsea and Arsenal — games United won by a margin of just one goal — have together given the Reds as many as 17 points that they might otherwise have left by the wayside.
In short, United might in a worst-case scenario without Van Persie have amassed as few as 22 points from 16 games, instead of the 39 it has now. Conceivably, United might have been marooned in the middle of the standings with the likes of Liverpool, West Ham and Norwich, all on 22 points, instead of sitting pretty at the top on a six-point cushion over second-placed City.
Of course, had he not signed Van Persie, Ferguson still would have had other players scoring goals, so it's impossible to be 100 percent sure how United would have fared without him.
But Van Persie has been digging United out of holes since he joined the club. The Reds have been shaky repeatedly this season, especially in defense, shipping 23 goals — just six fewer than Queens Park Rangers, in 20th and last place. So it is fact, not merely statistical theory, that United wouldn't be doing quite so well without Van Persie.
It's astounding to think that what United paid Arsenal for Van Persie is also roughly the fee City reportedly paid to Inter Milan for Mario Balotelli in 2010. Already, United can crow that it got by far the better deal and the better striker.
City was much better on Sunday without Balotelli than it was when he played. Only after City manager Roberto Mancini replaced the Italy forward in the 51st minute with Carlos Tevez, did the defending league champions look like a team with 11 players, not 10 plus a hanger-on who didn't seem to care.
Tevez looked determined to prove his worth against United, his former team that opted not to keep him. The Argentina striker's energy, industry and understanding in attack with Sergio Aguero were such that one had to wonder why Mancini hadn't started with Tevez, instead of Balotelli. If all the Abu Dhabi wealth pumped into City does not yield a repeat league title this season, it will be partly because of perplexing decisions like these from Mancini.
One also wonders whether the Italian's patience will now run out with Balotelli, who was so impressive 13 months ago when City thrashed United 6-1 but so lackadaisical Sunday.
Cruise, who said this was his first soccer match in England, must have noticed it and only with eyes wide shut could Mancini now fail to see it, too: Balotelli is no longer earning his considerable crust at City.
"When you have a player that has Mario's quality, you cannot understand why he continues to throw it out of the window. It is incredible," Mancini said. "I have seen players in my life with fantastic quality. But in the end, they did nothing. I don't want Mario to finish like these players."
Leading the league approaching midpoint in the season is no guarantee United will win it come May. Still, being the team that ended City's run of 37 league games unbeaten at home at the Etihad Stadium is a big boost for United. That it was United that snapped that streak will particularly sting for City and its fans. The red-blue divide cuts through Manchester — families and friendships — so defeats to the cross-town rival hit particularly close to home.
It is too early to be sure that the pendulum that swung from United, the 2011 champion, to City in 2012 is now swinging back to Old Trafford. Still, it was United that ended Arsenal's 49-match unbeaten streak in 2004 and Chelsea's 40-game unbeaten league run in 2005. Both those teams challenged United's dominance for a while before Ferguson beat them back down — as he now intends to do to City.
With Van Persie, Ferguson has the tool to quiet his noisy neighbor down.
John Leicester is an international sports columnist for The Associated Press. Write to him at jleicester(at)ap.org or follow him at http://twitter.com/johnleicester