كتب : Hatem Maher
"If your concentration isn't good at the back it can cause you problems," Ferguson was quoted as saying by United's official website after the game.
"And of course that's what happened tonight. Celtic's first goal was a lapse in concentration and it gave them a great boost."
Vennegoor of Hesselink gave the visitors the lead before two strikes by in-form French striker Louis Saha put United in front but Shunsuke Nakamura equalized just before the interval.
But Ole Gunnar Solskjaer came off the bench to score the winner from Saha's rebound, his first goal at Old Trafford for almost three years.
"It was a typical Solskjaer goal. He knew exactly where the ball was going to land before anyone else and was the first to react," the Scottish tactician said.
"It was a pure goalscorer's goal and it showed that he's still got a lot to offer this team."
United's victory was marred by the injury of Welsh winger Ryan Giggs’s injury.
"He's got a hamstring injury and will be out for three weeks," Ferguson said.