Sir Alex believes the tense 1-0 victory over Fulham was a "great game" for the champions because it will act as a warning for the remainder of the run-in.
The Reds will face similar battles against determined opponents in the weeks to come and, despite the experience of the side, a wake-up call could prove useful with the three points safely banked. After moving three points clear at the Barclays Premier League summit, the manager was happy to take the positives from a difficult evening.
"The matches are all challenges," he told Sky Sports. "That's a great indication. It was a great game for us tonight because that's exactly what it's going to be like for the rest of the season. Teams are going to be battling and fighting, trying to survive, and not be lambs to the slaughter to Manchester United because they don't want to be seen to be laying down.
"Fulham put in a massive effort tonight. They're a very experienced team and were very difficult to break down. When you sit back, it doesn't matter if you've got 11 plumbers, joiners or footballers, it's hard to break down. We did enough to finish the game off but didn't do it and nearly paid the penalty."
Penalty was a word on everybody of a Fulham persuasion's lips after Danny Murphy was sent tumbling inside the box in the closing stages by Michael Carrick. Referee Michael Oliver failed to point to the spot and Sir Alex felt another clear shout in the first half, for the hosts, may have been playing on the official's mind.
"I think they had a claim," added the boss. "No doubt.
"I think we had a claim for clear handball in the first half, maybe it was close to the attacker but it was a claim and Patrice Evra thought it was stonewall as he handled the ball going into the penalty box and denied an opportunity.