MANCHESTER United boss Sir Alex Ferguson has told his team they must be more clinical, despite claiming the leadership of the Barclays Premier League.

United moved to the top with a comfortable 2-1 victory over Arsenal at Old Trafford but Ferguson felt they should have had much more to show for their near total domination.

Robin van Persie struck against his old club inside three minutes, but despite a superiority in almost every facet of the game, United never threatened to repeat last season’s 8-2 humbling of the Gunners.

United missed a number of chances, including a penalty – Wayne Rooney dragging wide from the spot – but Patrice Evra made the scoreline more comfortable with a 67thminute header.

Yet even after Arsenal had Jack Wilshere sent off, United might still have faced a nervy finish had Santi Cazorla’s injury- time consolation come a couple of minutes earlier.

Ferguson said: ‘‘I’m disappointed with our inability to hammer home an advantage.

‘‘I spoke about goal difference at the start of the season.

‘‘We lost the title on goal difference last season and I don’t want to see that again. We had an opportunity to add to our tally.’’ The game lacked the intensity of some of the memorable clashes the clubs have fought out over the past decade, mainly because Arsenal were outshone.

Coming after last week’s ferocious battle with Chelsea, it was quite a flat encounter for United and Ferguson grew concerned as the game unfolded.

He said: ‘‘It looked as though it was going to be selfdestruction.

It only takes a second to lose a goal.

‘‘They had some possession without threatening us but thank God we got the second one because with them scoring right on time, it would have been an embarrassment.’’ Penalties are also a worry for the Scot, with United having now missed four of their six spot-kicks this season.

Ferguson said: ‘‘I think I will take it myself next week if we get one.’’ Arsenal’s defeat was their second in three league games and left them nine points off the top after their worst start in manager Arsene Wenger’s 16 years in charge.

Their agonies were compounded by the dismissal of Wilshere, who had been in just his second game back after a 14-month injury absence, for a second yellow card.

Wilshere had perhaps been lucky to escape a second booking earlier but his departure was inevitable after a bad challenge on Evra on 69 minutes.

United’s Tom Cleverley had found himself in a similar situation after some mistimed tackles, but Ferguson withdrew him for his protection.