In-form Antonio Valencia struck nine minutes from time to set up a typically patient win at relegation-threatened Rovers.
Substitute Ashley Young grabbed the second in style on 86 minutes to send United five points clear of rivals Manchester City with seven games left to play.
Second-placed City's 3-3 home draw with Sunderland on Saturday had given United the chance to ram home their advantage and they now look odds-on for glory.
But Ferguson remains cautious, despite his side's advantage.
"We've still got seven games left. In my experience of these situations, it doesn't matter what the points are at the moment," Ferguson said.
"It matters about next Sunday's game.
"It was a long night. We had to persevere and persevere. We got our rewards," he said.
"We weren't making any clear-cut chances for a long time.
"But it was an important win and it typifies the history of the club."
David de Gea was on top form, the keeper making three tremendous saves in the first half to prevent Rovers from taking the lead and Ferguson was quick to praise the Spaniard.
"The progress is obvious for all to see," he said.
"He's growing in stature and confidence. He made three great first-half saves.
"David kept us in the game. We had a lot of possession, but we just couldn't get that goal with the way Blackburn defended deep."
Defeat for Rovers saw them side slip into the bottom three on goal difference, but manager Steve Kean insisted he had seen enough fight from his side against United to suggest they have what it takes to beat the drop.
"If we can play at that standard for next seven games - not for 80 minutes but 90 - we'll get plenty of wins," he said.
"We've got to take all the positives out of the first 80 minutes. We've got to set that standard.
"We were playing against the potential champions.
"I think for 80 minutes we gave it a really good go. Their goalkeeper has had a very good night. He's made good saves when we've had our little opportunities.
"I thought (Junior) Hoilett and Yakubu caused them problems."
United, who lost to local rivals Blackburn at home in December, can extend their lead on Sunday at home to Queens Park Rangers before City visit Arsenal.