Brendan Rodgers' men headed into the quarter-final tie with six wins from their last seven matches in all competitions.
But they endured a frustrating afternoon against their Championship opponents, creating little of note in the first half after their defender Martin Skrtel required extended medical attention following an aerial challenge with Blackburn frontman Rudy Gestede.
Raheem Sterling got back to block Gestede as the striker wound up a volley, the ball striking the England man's hand but prompting no penalty appeal from Blackburn.
Toure was caught out of position on that attack and he was soon involved at the other end, converting Daniel Sturridge's set-piece knockdown from an offside position.
Blackburn goalkeeper Simon Eastwood was under employed during the first half but reacted sharply to beat away a venomous shot on the turn from Sturridge during the seventh of eight minutes added on for Skrtel's injury.
Mignolet needed a save of the highest quality to keep out Alex Baptiste’s header from Conway's 49th-minute corner.
The game's latest marginal penalty shout arrived in the 55th minute as Kilgallon put his arm across Sturridge and the England striker went down. Again, referee Andre Marriner was unmoved.
Toure almost broke the deadlock as the hour approached, heading Philippe Coutinho's free-kick from the left into the turf and against the right-hand post.
In the 73rd minute, Baptiste misjudged a defensive header but Sturridge could only blast wide of the near post.
As they did in round four after being held by Bolton Wanderers, Liverpool must now travel to a Championship club to progress, while Blackburn retain hopes of repeating their giant-killing feats of two seasons ago against Arsenal.
