Sir Alex Ferguson admitted his tactics backfired as Manchester United were forced to come from behind to avoid an embarrassing defeat at Southampton in the FA Cup fourth round.
The npower League One side bossed the first half and deservedly broke the deadlock on the stroke of half-time, with Richard Chaplow smashing Saints ahead.However, Ferguson's introduction of Nani and Ryan Giggs 13 minutes into the second half gave United impetus and goals from Michael Owen and Javier Hernandez turned the tie around.
"Sometimes we make it difficult for ourselves but, in fairness, I maybe meddled with the system somewhat," he told MUTV. "We tried a diamond in the middle of the pitch and, of course, Manchester United are used to playing with width all the time and I think that was a problem for us."
He added"It wasn't working at all. We had some possession of the ball but we never really threatened. We had two or three shots from the edge of the box.
"It was a nothing first half, really, and the goal, if anything, made us play. (Southampton) scoring the goal right on half-time motivated us a bit to do better."
Ferguson admitted the timing of Owen's goal was important to ensure the game did not get away from them, while he praised Hernandez for his clinical finishing, saying: "He only had one chance: one chance, one goal."
Southampton manager Nigel Adkins, meanwhile, expects precocious winger Alex Oxlade-Chamberlain to remain at St Mary's for the rest of the season.
Speculation over the 17-year-old's future has been rife throughout January, with Arsenal and Liverpool mooted as a potential destination. However, Adkins insists that Southampton have no intention of selling him despite interest from some of the Barclays Premier League elite.
"We are not envisaging selling him, we're not looking to sell him," he said after the match. "We don't want to sell him. I think it is beneficial for him to be playing regularly for Southampton in the Football League, giving him a chance to develop.
"Yes, he is well courted and you can see that he has ability about him. Southampton Football Club are not looking to sell Alex Chamberlain."