The Reds will now switch to ensuring victory in the title race and what would be the club's 20th league crown. Sir Alex's men currently hold a 15-point lead over rivals Manchester City who are United's next opponents at Old Trafford on Monday.
"We must kick on," insisted Sir Alex. "We're disappointed and the players are down. They're disappointed because they know they can do better.
"To be honest with you, for the ninety minutes I thought only Antonio Valencia reached the standard that we expect of them. Phil Jones, for a good part of the game, and David De Gea did well. But in terms of the ninety-minute performance, Antonio was the only one.
"But we need to forget this result and look forward to the game with City. A positive result for us next Monday will just about seal the title for us."