But Ferguson refused to get carried away after Cristiano Ronaldo's first-half penalty earned his side a seventh straight league win.
"The important thing is we keep the form going," said Ferguson. "We have a difficult game away to West Ham next week. All teams drop points in the run-in. We just hope we don't drop as many as the rest.
"It's an advantage (being top). It's not a great advantage because there are still 15 games left. But it's always better to be top of the league than anywhere else."
Having started January third in the table, United ended the month with a significant advantage over closest challengers Liverpool and Chelsea and a game in hand.
Michael Carrick, sent tumbling by Mikel Arteta in the 44th minute for the spot-kick which allowed Ronaldo to notch his 13th goal of the season, said: "Who know how decisive our five-point advantage can be?
"We've done our bit this weekend," added Carrick. We're happy with 1-0, we've got another clean sheet and we had chances to score a few more."
And the England midfielder was adamant that United had yet to hit top form.
"We can be satisfied with the three points, but there's still more to come from us."
United's latest victory saw their Dutch goalkeeper Edwin van der Sar set an all-time English record for the most number of minutes without conceding a league goal.
His latest clean sheet meant Van der Sar had not conceded a goal in 18 hours and 42 minutes of action in the top tier. Samir Nasri was the last player to beat the 38-year-old in the Premier League during Arsenal's 2-1 win in November.
Ferguson said the consistency and excellence of his goalkeeper had made his team's job in overhauling Liverpool at the summit much easier.
"The composure he brings, the experience he brings, Edwin has been outstanding for us," said Ferguson.
"I couldn't believe it when I read that the last goal we conceded in the league was at Arsenal back in November. It's incredible. Edwin brings a calm and an assurance to the players in front of him.
"I don't know how many times we have had to change the back four over the last 12 games.
"But the record says a lot for the players that have come in. You really have to pay credit to Edwin."