Midfielder Dack picked up the ball on the edge of the box and after feinting to shoot on his left, cut back and let rip with a right-footed shot that deflected off Shaun Hutchinson giving Bartosz Białkowski no chance.

Millwall looked lost for ideas going forwards and nearly put more pressure on themselves when Białkowski’s attempted clearance hit Tyrhys Dolan in the box but the ball just ran away from Ben Brereton, who was coming back from an offside position.

Blackburn had one more chance to extend their lead before the break when Barry Douglas curled a set-piece in with his left foot and Gallagher did well to get up highest and meet it, but his header looped well over the bar.

Gary Rowett opted to change his mode of attack just before the hour mark, introducing Matt Smith off the bench and the big striker almost made an immediate impact but could not direct Scott Malone’s cross on target.

Malone then had an opportunity to test Thomas Kaminski himself but his free-kick was straight at the Belgian and moments later Blackburn spurned a chance of their own as Gallagher’s effort was easily saved by Białkowski.

As 70 minutes approached John Buckley outpaced the Millwall defence to reach the byline and cut it back for Dack, who was charging in and looked hampered by a challenge from Ryan Woods as he shaped to shoot.

A corner was signalled by referee Matthew Donohue but Dack and his teammates were convinced it should have been a penalty.

Both managers then made triple substitutions and it was Liverpool loanee Harvey Elliott who made the biggest difference for Blackburn.

The 17-year-old burst into the box and fed fellow teenager Dolan, whose shot deflected off Jake Cooper, onto the chest of Gallagher and into the back of the net – although the Rovers striker knew very little about it.

The hosts almost got themselves back into the game late on when George Evans struck the upright and Kaminski smartly righted himself to keep out Jon Dadi Bodvarsson’s follow up.