Sir Alex Ferguson is concerned Manchester United's wastefulness in front of goal could cost them at the end of the season.
United missed a penalty and a host of other chances in their 2-1 Premier League win over Arsenal on Saturday.
"We lost [the title] on goal difference last season and I don't want to see that again," said United boss Ferguson.
"I'm disappointed with our inability to hammer home an advantage - we should have won by four or five."
United kept Arsenal goalkeeper Vito Mannone busy throughout the game and the Italian, standing in for the injured Wojciech Szczesny, made superb saves from Robin van Persie, who scored United's first goal, and Wayne Rooney.
The England striker also sent a penalty wide while Antonio Valencia missed an open goal.
"It was a strange game. We had an opportunity to add to our tally," said Ferguson. "It looked as though it was going to be self-destruction. 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."
Rooney's failure from the penalty spot means United have now missed four spot kicks from six attempts this season.
"I think I will take it myself next week, if we get one," said the Scot. "When you take a penalty you should hit the target so at least the goalkeeper has to save it.
"Normally Wayne can hit great penalties, but that was a bad one, he knows that."
Defender Rio Ferdinand echoed his manager's disappointment after the match.
"If you had been in our changing room you'd have thought we lost the game, the way the mood was," he said.
"We should have finished that game off ages ago. That is the most disappointing thing."