A Cristiano Ronaldo penalty on 20 minutes, a Lloyd Doyley own goal and strikes from Henrik Larsson and Wayne Rooney gave United a comfortable win despite resting several players.
Chelsea, now on 54 points, did their bit with Didier Drogba notching his 15th league goal of the season on six minutes when he picked up Frank Lampard's weighted pass and drilled a left-foot shot into the bottom corner.
The impressive Andriy Shevchenko was twice denied but Blackburn also threatened and could easily have grabbed an equaliser against Chelsea's recently shaky defence.
Benni McCarthy missed a header for the visitors, who also had a penalty appeal turned down, while Ricardo Carvalho was forced to clear Matt Derbyshire's effort of the line.
Lampard killed off Blackburn's hopes though midway through the second half when he belted in a trademark 30 metre shot before Salomon Kalou scored late on.
It was not all good news for champions Chelsea. England left back Ashley Cole was stretchered off with what looked like a serious injury after jarring his knee.
OWN GOAL
Ronaldo continued his personal battle with Drogba for the golden boot by bagging his 14th league goal of the season after Ole Gunnar Solksjaer was fouled by Jay DeMerit.
United, who rested Edwin Van der Sar, Ryan Giggs and Paul Scholes, increased the tempo after halftime and forced Doyley to head into his own goal on 61 minutes before Larsson scored his first Premier League goal and Rooney netted a superb lob.
"We've got a good squad of lads. There's a great spirit among them," Ferguson told Sky Sports News before confirming there would be no late bid for Bayern Munich's England midfielder Owen Hargreaves.
In other games on Wednesday, Newcastle United beat Aston Villa 3-1 despite Villa having the best of the game for long periods. Relegation-threatened Charlton Athletic drew 1-1 at Bolton Wanderers.
On Tuesday, Liverpool put themselves back in the championship picture with a 2-1 win at struggling West Ham United.
