The 36-year-old scored his first goal of the season early on and added his second midway through the second half as the blundering Lions gifted a confident home side the most emphatic of wins.

Boss Scott Parker made eight changes to the side that started in Wednesday’s 2-2 draw with Manchester United and they did not disappoint, as further goals from Loum Tchaouna and Jaidon Anthony put them out of sight by half-time.

Substitute Jaydon Banel added Burnley’s fifth on the stroke of 90 minutes before the shell-shocked Lions, who had completely capitulated, netted an added-time consolation through Josh Coburn.

Burnley dominated the opening exchanges and grabbed the lead in the 11th minute when Jacob Bruun Larsen squared for Barnes to sweep home past visiting goalkeeper Steven Benda.

The Lions mustered little in response, with Aidomo Emakhu booting their best chance straight at Burnley keeper Max Weiss after being released down the left by Joe Bryan.

But the visitors slowly grew into the game and should have levelled when Jake Cooper got his head on Alfie Doughty’s cross from deep on the left but was denied by a brilliant over-arm save from Weiss.

The keeper saved again from Cooper on the half-hour as Millwall threatened a leveller but the visitors were undone by two defensive errors that put the game beyond their grasp.

Tchaouna was allowed to thread his left-foot shot from the edge of the box past a static Benda on 35 minutes and shortly before the break the Millwall keeper’s poor clearance ultimately gifted Anthony the chance to slide home his side’s third.

Millwall looked livelier at the start of the second half and Thierno Ballo should have done better when he found space to get a shot off in the left side of the box, but the home side were clearly in cruise control.

Tchaouna came close to his second when he rifled a shot against the outside of Benda’s right-hand post and the increasingly inevitable fourth arrived on 65 minutes when Kamarl Grant made a hash of clearing Anthony’s right-wing cross and a delighted Barnes mopped up.

Hunting for a hat-trick, Barnes flashed a header straight at Benda as the linesman’s flag was raised, but it was Banel who completed the rout from close range before Coburn’s confident finish in stoppage time.