Roberto Mancini may be kidding himself about how close he came to signing Robin van Persie in the summer – when the new arrival from Arsenal spoke about the little boy inside him screaming to join Manchester United it sounded as though his heart had long been set on a move to Old Trafford – but it is easy to see why the Manchester City manager has just expressed his disappointment at missing out on such a reliable goalscorer.

Mancini knows what the Premier League season is making increasingly obvious and that is that Van Persie could be the difference between the two Manchester clubs come May. It was always likely that a proven scorer would come in handy at either of the two sides who needed to be split by goal difference last season and though City could almost certainly have financially topped any United offer it appears that the little boy who swung the decision United's way could also have the same effect on the title argument.

With Van Persie in the side United are already 19 goals to the good and counting. They have acquired an immunity to those off days of old when the absence of Wayne Rooney would leave them seriously short of ideas and firepower and they can instantly dig themselves out of situations when not everything is going their way. One moment of class from Van Persie ensured normal service returned at Wigan, a ground where United have always been in the habit of scoring four or five but where an unexpected defeat near the end of last season cost them dear.

Roberto Martínez's side never looked capable of pulling off another such upset here. They began the game passing neatly enough without managing to find the precision pass to hurt their opponents in the final third, whereas United looked fairly ordinary at times in midfield yet had undoubted quality up front.

Javier Hernández scored his 11th and 12th goals of the season with two trademark predator's finishes though it was the goal sandwiched between them, with the game still delicately poised, that showed Van Persie's true worth. United got a lucky break down the right when Maynor Figueroa and James McArthur collided with each other to leave Hernández with a clear run up the wing, yet there was still plenty of work to do when the cross arrived at Van Persie's feet.

Reacting more coolly than the Wigan defenders who were frantically trying to close him down, Van Persie gracefully allowed Iván Ramis to slide harmlessly past, before pushing the ball around Gary Caldwell to open up space for a shot, which was promptly struck past Ali al-Habsi before the goalkeeper had time to respond. It was, at the same time, a difficult chance and a goal from the moment Van Persie received the ball, which is always the mark of a class striker.

Van Persie also struck the free-kick from which Hernández scored his second and he put a shot too high in the second half before grabbing United's fourth goal at the end when Danny Welbeck served him a chance on a plate. "He's fantastic, a completely rounded footballer," said Sir Alex Ferguson.

That is not to say Van Persie was United's only source of inspiration. Hernández obviously played his part too, not only in scoring two close-range goals but helping create the other, while Ryan Giggs was arguably the neatest midfielder on view and Jonny Evans was again highly impressive. The defender had the pace and anticipation to help Giggs out when the midfielder lost the ball to Arouna Koné on half way in the first half, though you would expect that. He also had the presence of mind and the passing accuracy to play in Patrice Evra at the other end for the shot that led to United's opening goal.

The harshest critics might carp that this was another low key, low-voltage Manchester United performance with little of the usual drama, defending well and accepting scoring opportunities eliminates the need for drama. But it was also a second consecutive clean sheet, a third consecutive win, a return to the healthy habit of handing out drubbings to Wigan and – perhaps most significant of all – a 10 points out of 12 return from four festive fixtures in the space of 10 days. That is the sort of stamina it takes to win titles and it helps if you can take chances to kill games.

It is unlikely that the little boy inside Van Persie ever dreamed about scoring goals to help win titles on rainy days in Wigan and it is far too early in to make any such claims around this result. However, one by one United are avoiding last season's pitfalls and allowing pressure to build on their rivals.

"We didn't have the legs today, and United did," Martínez lamented. "They have a talented squad and were able to make five changes, so were much fresher. We were always second to the ball. The goals we conceded didn't come from outstanding play but Van Persie looked fresher than our whole backline."