The Blue and Whites provided a step up in quality from the Reds' first three opponents, but they could not sustain their bright start and soon faded away.
After missing from the penalty spot and hitting the post in the first half, Liverpool stepped things up in the second half with a completely different outfield side, claiming the win in East Lancashire through goals from Lazar Markovic and Daniel Sturridge.
Jurgen Klopp's charges, unbeaten in four summer outings, will now head to the United States for high-profile friendlies against Borussia Dortmund, Manchester City and Manchester United.
James Milner wasted a big chance to put Liverpool in front inside the opening six minutes, as his penalty was well saved by David Raya after the goalkeeper took out Dominic Solanke once played through on goal.
A half-chance also came and went for Divock Origi, who failed to keep his half-volley on target, but Blackburn were also having the odd positive moments in a quiet first half.
Having had to ride their luck a little, Liverpool ended the opening 45 minutes the stronger side and should have taken a lead into the break.
Lallana's delicate chip came back off the frame of the goal, and when the ball came back into the middle he was denied by Charlie Mulgrew on the line.
For the fourth friendly in a row, Klopp made mass changes to his lineup at the midway point, retaining only Karius for the second period - and even he was replaced by Caoimhin Kelleher with an hour played.
One of those to be introduced at the break, England international striker Sturridge, sent a shot across the face of goal and then slotted wide from a better opening five minutes later.
Liverpool's tempo was much improved in the second period and they were rewarded with a goal 63 minutes in, with forgotten man Markovic thumping Sturridge's through-ball out of replacement keeper Jayson Leutwiler's reach.
Blackburn, winless in their last four competitive meetings with tonight's opponents, continued to fade as the match wore on.
Naby Keita won the ball high up the field and slipped it through for the Englishman, who needed one touch to control the ball and a second to tuck it home.
The lively Keita was keen to get off the mark and came close to doing so when sending a shot rising over the bar 15 minutes from time, but Liverpool had to settle for just the two goals on the night.
BLACKBURN ROVERS (4-2-3-1): Raya (Leutwiler 60'); Nyambe (Conway 60'), Lenihan (Downing 60'), Mulgrew (Bell 46'), Williams (Wharton 60'); Evans (Travis 46'), Smallwood (Davenport 60'); Bennett (Tomlinson 60'), Dack (Nuttall 60'), Rothwell (Whittingham 60'); Samuel
LIVERPOOL FIRST-HALF XI (4-3-3): Karius; Clyne, Matip, Klavan, Moreno; Milner, Lallana, Woodburn; Ojo, Origi, Solanke
LIVERPOOL SECOND-HALF XI (4-2-3-1): Karius (Kelleher 63'); Gomez, Phillips, Van Dijk, Robertson; Fabinho, Jones; Keita, Camacho, Markovic; Sturridge