The prolific Netherlands striker did little to dispel that theory Tuesday.
Van Persie ushered in 2013 by taking his league-high tally to 16 goals with a brace in United's 4-0 win at Wigan, maintaining the team's seven-point lead over City. Javier Hernandez also scored twice but Van Persie stood out again, scoring a sublime strike with his weaker right foot for the pick of the goals.
"We expected him to be a major player and add something to us and that is exactly what he has done," said United manager Alex Ferguson, who spent 24 million pounds (then $38 million) on signing Van Persie from Arsenal in August.
"Robin is a completely rounded footballer."
City also made a statement of intent to kick off the new year, easing past Stoke 3-0 at home, but is now relying on some slip-ups from United. At the moment, they don't look like coming.
"We have just got to continue to win football matches," City assistant manager David Platt said.
Goals by Pablo Zabaleta, Edin Dzeko and Sergio Aguero at the Etihad Stadium ended Stoke's 10-match unbeaten run. However, a hamstring injury sustained by Aguero late on saw the game end under a cloud for City.
Tottenham climbed provisionally to third, above Chelsea by a point, by beating Reading 3-1 after having fallen behind in the fourth minute. Arsenal is provisionally fifth after a disappointing 1-1 draw at Southampton, needing an own goal to earn a point.
At the bottom, struggling Aston Villa ended a run of three heavy defeats by drawing 2-2 at Swansea but will rue conceding an equalizer deep into stoppage-time by Danny Graham.
Out-of-form pair Fulham and West Ham both won 2-1, against West Bromwich and Norwich, respectively, to stop their slide toward the relegation zone.
Van Persie, who could have signed for City last summer, showed once again why he could be the determining factor in this season's title race.
His goal that made it 2-0 was thunderously struck into the corner and arguably his best this campaign, and he rounded off a dominant win at the DW Stadium with his 19th goal in all competitions.
"He came to us at the very peak of his career," Ferguson said. "His ability to make and take goals is fantastic."
With Wayne Rooney still absent because of a knee ligament injury, Hernandez was given another opportunity up front and he didn't waste it, displaying his predatory instincts with goals in the 35th and 63rd minutes. It left Wigan with no chance of repeating its surprise home win over Ferguson's side last season.
Another second straight clean sheet also pleased Ferguson, whose defence has been heavily criticized this season after conceding more goals than any other team in the top half.
City did its job by crushing Stoke to keep the pressure on its neighbour, although it proved to be a bittersweet match for Aguero.
The Argentina striker completed the scoring by converting a 74th-minute penalty but hobbled off with a hamstring injury that is likely to keep him out for City's next two matches.
Mancini, though, will be happy with the way his team comfortably saw off an opponent that hadn't been beaten in its previous 10 games. Aguero could easily have come away with a hat trick, only to find Stoke goalkeeper Asmir Begovic in fine form before his resistance was breached by right back Zabaleta in the 40th.
With Chelsea not playing until Wednesday, against last-place Queens Park Rangers, Tottenham didn't waste a chance to rise above its London rival.
Pavel Pogrebnyak put Reading ahead early but Michael Dawson equalized, Emmanuel Adebayor headed powerfully in for 2-1 and Clint Dempsey added a deflected third.
"We did well to close out the festive period with 10 points from four games and hopefully we will continue this form to put ourselves in the position we want to be," Tottenham manager Andre Villas-Boas said.
Spurs are five points ahead of fifth-place Arsenal, which produced a flat display at relegation-threatened Southampton and fell behind to Gaston Ramirez's 34th-minute goal.
Guly do Prado turned Theo Walcott's free kick into his own net seven minutes later for Arsenal's equalizer but the visitors were outplayed at times by the home side, which climbed out of the bottom three with the draw.
Dimitar Berbatov was at his delightful best for Fulham, the languid Bulgarian striker scoring one and running rings around West Brom's defence in a vital win at the Hawthorns. Sweden winger Alex Kacaniklic grabbed Fulham's 58th-minute winner, ending his team's four-match winless run that had dropped it close to relegation trouble.
Norwich slipped to a fourth straight league loss after conceding first-half goals to Mark Noble and Joey O'Brien for West Ham, rendering Russell Martin's late goal a consolation.
Villa finally earned a point at the end of a chastening festive schedule, in which it had conceded 15 goals in three big losses, but Paul Lambert's side still won't be happy.
Christian Benteke looked to have given Villa victory by converting an 84th-minute penalty at the Liberty Stadium for 2-1 but Graham scored in a goalmouth scramble four minutes into injury time to grab a deserved point for Swansea.Suggest a correction