First-half goals from James Henry and Rob Hulse and a second-half strike from Danny N’Guessan ensured the Lions progressed to the last eight of the tournament for the first time since they were beaten in the 2004 final by Manchester United.
Luton manager Paul Buckle made two changes from the side that beat Norwich in round four, with Jonathan Smith, JJ O'Donnell and Scott Rendell coming in to the side, while Millwall were rocked by a late injury to captain Danny Shittu, with Karleigh Osborne coming in to replace the Nigerian centre-back.
It was the visitors who had the first clear chance of the game after just two minutes, as veteran striker Hulse beat the offside trap to find himself one-on-one with Hatters keeper Mark Tyler, but the QPR loanee could only drag his shot wide of the far post from 16 yards out.
LUTON 0-3 MILLWALL
However, it was the Championship side who got the first goal of the game after 11 minutes when Henry capitalised on a woeful mistake from Luton defender Janos Kovacs. The Hungarian centre-back failed to control a simple pass and the quick-witted Henry pounced on the loose ball, before advancing on goal and rounding the stranded Tyler to put the Lions ahead.
The non-leaguers almost bounced straight back through Arnaud Mendy when the midfielder reacted quickest to a headed knock-down in the area to lash a shot towards goal, however, Forde reacted well and beat his effort away to safety.
Millwall then began to take control of proceedings and it came as little surprise when they grabbed a second goal 10 minutes before half-time. It came through Hulse, who more than made up for his earlier miss with a wonderful volleyed effort from just inside the six-yard box.
Henry did well in the build-up down the right and hung a cross towards the far post where Hulse first won a header, before finding the net with an improvised overhead kick which nestled into the bottom corner of Tyler’s net.
That was the final drama of the opening period, and the second half began in much the same fashion as Luton struggled to get a foothold in the game.
They did come close to cutting the deficit 10 minutes into the half, however, with Kovacs getting up well to win a header at a corner, but his powerful effort narrowly cleared Forde’s crossbar.
The visitors were stifling the midfield and making it hard for the Hatters to get back into the contest, and they almost grabbed themselves a third goal midway through the second half when Andy Keogh reacted quickest to a deflected shot from substitute N’Guessan, but the Irish striker could only shoot over the crossbar from close range.
Millwall’s hunt for a decisive third continued as the game wore on, and Keogh will have been scratching his head in disbelief at how he failed to score after first seeing a header well saved by Tyler, before somehow heading wide when it looked easier to score just minutes later.
With just five minutes left, Millwall made the game safe when N'Guessan reacted quickest to a fumble from Hatters keeper Tyler to stroke home from close range and ensure the scoreline gave a more accurate reflection of the game's proceedings.