With striker Wayne Rooney sidelined for four weeks with an ankle injury, Ronaldo stepped up and carried the scoring load for the Red Devils, who moved three points clear of Arsenal at the top of the table with the win.
Arsenal will travel to Reading on Monday to try and move back level on points, but it was Ronaldo's two goals in one minute that allowed United to move ahead.
Blackburn created the first chance of the game 19 minutes in when Ronaldo lost possession in his own end, which allowed Christopher Samba to have a strike on goal from 30 yards. The Blackburn defender got plenty of pace on the shot and had United keeper Edwin Van der Sar easily beaten. However, the ball came back off the crossbar and the game was still scoreless.
After holding off United over the first 30 minutes, Blackburn suffered a lapse in defense and allowed United to score twice within a minute.
The first goal came from a corner kick that Ryan Giggs curled into the box and Ronaldo got up to head on target from the penalty spot. Blackburn's David Bentley was positioned on the left post, but he could only get a slight touch on the ball with his head as it sailed into the upper corner.
Less than one minute later, Ronaldo added his second goal of the game on a nice counter attack. Louis Saha got hold of the ball in midfield and knocked it wide to Carlos Tevez on the left. The Argentine then played Ronaldo into the box on the right, and he finished off the play by sliding the ball across the face of goal and into the lower left corner.
The flurry put United up two goals at halftime despite a mostly strong first half from Rovers.
The second half did not start well for the visitors and they soon had any hope of a comeback snuffed out shortly after the break. David Dunn had picked up a yellow card in the first half, and it only took him eight minutes into the second half to get a second. Dunn came in hard on Saha from behind and he was shown his second yellow card, ending his game early.
Blackburn did well not to concede another goal with only 10 men, but they also were unable to create much in attack, and they could not avoid their second loss of the season.
Chelsea had a chance to move level with Arsenal if they could beat Everton at Stamford Bridge, and after 70 minutes of play, it looked good as Didier Drogba put Chelsea ahead with a fine header. However, Tim Cahill stunned the home side with a brilliant overhead kick that beat keeper Carlo Cudicini from six yards out to level the match at 1-1 in the 90th minute, forcing Chelsea to settle for a draw.
Bolton and Middlesbrough played to a 0-0 draw at the Reebok Stadium, while Aston Villa got a late winner from Gabriel Agbonlahor to pull out a 2-1 win at St Andrews Stadium against Birmingham.
Tottenham moved up to 14th in table with a resounding 4-0 win against Wigan as Jermaine Jenas scored two goals while Manchester City stayed one point ahead of Chelsea in third place with a 0-0 draw at Portsmouth.