City thrashing was a wake-up call: Ferguson
A first half goal from Javier Hernandez earned United a valuable 1-0 away victory at Swansea City on Saturday.
"The game against Manchester City was a wake-up call for us," said Ferguson. "Over the years our defence has been an integral part of our success and I thought we did well in that area.
"Swansea are a good footballing side and they keep the ball well. Against a side like that, you have to be concentrating all the time," he added.