However, Christiano Ronaldo's majestic free-kick on the hour mark settled the issue, although there were some nervous moments for United after that.
"When we were in a controlling position we gave away a really bad goal," Fergie siad after the 2-1 win.
"When you consider how we've defended over the past few weeks, that's not indicative of our performances.
"They became very determined in the second half and put on a real show and made it a fight for us.
"Sometimes when you don't play your very best you can get a result like that and it goes some way to winning the title, hopefully."