Wayne Rooney struck in the second half to clinch a valuable three points that puts pressure on rivals Manchester City, who play Liverpool on Sunday.
“It's an excellent result for us and I'm very pleased with that,” said Sir Alex. “They've had a great home record over the years and that's a really important result for us. It's a good position [being ten points clear], we're pleased.
"It was a fantastic, battling performance," he told MUTV. "There was a great determination about us. I thought they were really up for it, the players, making sure they weren't going to lose the game.
"This is not an easy place to come to, as everyone knows, and over the years they've been difficult to beat here. It's a good performance, a really good game, an important result... they're all important now. It's three points for each team you play against, it doesn't matter if it's the top, the bottom or the middle, they all count."
Rooney got the crucial goal with little over ten minutes remaining, but David De Gea’s key saves and the willingness of United’s back four to put their bodies in the way of shots and crosses was equally influential.
“When you look at our performance, you saw players who were prepared to put their body on the line," the boss added in an interview with ESPN. "We blocked shots, had great headers out of the defence, it was a really determined effort by the players and we still played our football into