It was the day Dimitar Berbatov reminded Manchester United why he finished as the joint winner of last season's Golden Boot. This was the first time he has started a league fixture since September, and it can all feel faintly ludicrous when he scores goals with this level of expertise.

Berbatov, lest it be forgotten, has been marginalised at Old Trafford to the point he can start talking to potential buyers from Sunday onwards, only six months away from being a free agent. After three months on the edges he needed a big performance and it was duly delivered on a day when Wayne Rooney stepped aside to let him complete his hat-trick from the penalty spot and the champions recorded their second successive 5-0 win to pull level with the leaders Manchester City. In the space of 16 days Alex Ferguson's team have clawed back a five-point deficit while closing the gap in terms of goal difference from 17 to five. They have a golden chance to go top against Blackburn Rovers on New Year's Eve, the manager's 70th birthday.

In the process they continued their run of immaculate results against Wigan: now played 14, won 14, scored 45 and conceded four. Yet the latest rout had a note of controversy attached and Wigan were entitled to feel aggrieved after being left painfully vulnerable by Conor Sammon's red card six minutes before the interval and the latest example of Phil Dowd's erratic officiating.

Ferguson's team were leading 1-0, courtesy of Park Ji-sung's eighth-minute goal, when Dowd ruled that Sammon had swung an elbow into Michael Carrick's face, and from that point it quickly became a case of how many goals the home side could accumulate. Roberto Martínez, the Wigan manager, described it as "an incredible call" and a "shocking decision", coming just at the point when his team were having their first good spell. Ferguson described it as "harsh" and it was rare to see Martínez so angry and outspoken.

Berbatov doubled the home side's lead within two minutes, latching on to Darron Gibson's cross and holding off Antolín Alcaraz before swivelling and shooting all in one moment, sending a left-foot shot past Ali al-Habsi. His second, 13 minutes into the second half, was even better, starting with the exquisite first touch to control Antonio Valencia's pass, evade Gary Caldwell and give himself the shooting chance. The shot was still rising as it hit the roof of the net but an aggrieved Martínez was not among those wanting to congratulate the Bulgarian. Berbatov, he said, had used exactly the same technique as Sammon had when backing into Carrick.

Valencia scored the fourth with a wonderful diagonal shot on the run, thumping Carrick's lay-off through a congested penalty area, and Rooney's generosity as United's usual penalty-taker allowed Berbatov to get his third after the increasingly vulnerable Alcaraz had tripped Park inside the penalty area.

Wigan had played quite brightly until the sending-off and responded well to Park turning in the opening goal after a fine run on the left from Patrice Evra. In truth, their record against United is so abject it was difficult to imagine United surrendering their lead anyway. Yet on another day this could have been an opportune time to play at Old Trafford and Martínez was right when he said it had changed the entire complexion of the game.

This was an unorthodox and experimental United line-up, with Gibson handed a rare start and only two senior defenders, Jonny Evans and Patrice Evra, available. Phil Jones and Chris Smalling had reported ill on Christmas Day, while Rio Ferdinand's back problems also resurfaced in training, meaning Carrick dropped back to play at centre-half and Valencia was used at right-back. Evans went off with a calf injury after a first half in which he found Victor Moses a difficult opponent, meaning he will be out for two weeks, and it left Evra at centre-half and the 19-year-old Zeki Fryers at left-back in a defence that, as Ferguson pointed out, had "never played together in their lives."

The sense was of a team that likes to show it can cope in difficult times and, though Martínez had every right to complain about Dowd, Wigan's grievances with the referee were undermined a little by the fact he had also missed a 16th-minute penalty for Alcaraz's hack at Javier Hernández's ankles.

As for Rooney, he was restricted to a substitute's role and played in midfield when he was introduced after 64 minutes. United had a full XI missing through injury or illness and, in the circumstances, they can reflect on a hugely satisfying December. Barring a shock against Blackburn, it will finish with them looking down on Manchester City.