Robbie Fowler scored his fourth goal in five games to extend Liverpool's winning run to seven matches.
Fowler strengthened his case for a long-term Liverpool deal
Fowler slotted into an open net from Fernando Morientes' pass after the offside Djibril Cisse was adjudged not to have interfered with play.
Cisse could have doubled the Reds' lead on the stroke of half time but Brad Friedel turned his strike onto the bar.
Blackburn piled on the pressure in the second half as Liverpool retreated but failed to seriously trouble Jose Reina.
The win means that Liverpool now only need one point from their remaining three fixtures to secure Champions League qualification.
Liverpool were without their influential captain Steven Gerrard who pulled out of the squad with a tight hamstring before kick-off and Peter Crouch and Harry Kewell were surprisingly left out of the line-up.
And their absence made for a toothless Liverpool attack for much of the first half.
Blackburn looked the most threatening and Rovers' energy and hustling in midfield forced Liverpool onto the back foot.
But for all Blackburn's industry, the home side were lacking the killer pass that Craig Bellamy was constantly searching for.
And it was the visitors who seized the initiative after 29 minutes.
Their opener was clouded in controversy as the referee's assistant allowed play to continue as Fowler controlled for Cisse who was standing in an offside position.
The France international striker let the ball run for the overlapping Morientes who coolly and unselfishly squared for Fowler to side-foot into an open net.
On the stroke of half time former Liverpool goalkeeper Friedel kept out Cisse's strike by turning it onto the bar when the forward was clean through.
It would have been harsh on the home side to go into the break two goals down and as the half-time whistle blew Rovers' tempers began to fray with Lucas Neill booked for a horrific challenge on Cisse.
Ryan Nelson saw a flicked header drift narrowly past the post and Robbie Savage slashed a volley wide as the home side probed for an equaliser.
Blackburn boss Mark Hughes introduced Shefki Kuqi to intimidate the resolute Liverpool defence but Morientes almost put the result beyond doubt with a close-range header that just went wide.
Cisse had a better chance to seal it at the end but he could only hit the post after being put clean through.
Rovers pushed for an equaliser but failed to break down the solid Liverpool resistance as boss Rafael Benitez celebrated his 46th birthday with a victory.
Liverpool manager Rafael Benitez:
"I was most pleased with the team spirit and our plan worked very well for us.
"We knew they had very quick players up front so we sat back and tried to hit them on the counter attack.
"You need to create the majority of chances in games like this and that is exactly what we managed to do."
Blackburn boss Mark Hughes:
"In my view the decision was incorrect. Cisse was interfering with play as he made a move towards the ball.
"The decision changed the shape of the game and the rule is very unclear.
"We stuck at it and tried to draw Liverpool out but they protected their lead and just went deeper and deeper."
Blackburn: Friedel, Neill, Khizanishvili, Nelsen, Gray, Bentley, Savage, Reid, Pedersen, Dickov (Kuqi 67), Bellamy.
Subs Not Used: Enckelman, Emerton, Mokoena, Peter.
Booked: Savage, Bentley, Neill.
Liverpool: Reina, Finnan, Carragher, Hyypia, Warnock (Kewell 69), Cisse, Sissoko, Alonso, Riise, Morientes (Kromkamp 81), Fowler (Luis Garcia 63).
Subs Not Used: Dudek, Traore.
Booked: Sissoko, Alonso.
Goals: Fowler 29.
Ref: A Wiley (Staffordshire).