Fred Onyedinma's 63rd minute header secured a vital three points for Millwall in Saturday's afternoon Sky Bet League One encounter with Southend United.
Neil Harris made four changes to his starting line-up from last Saturday's 2-0 victory over Coventry City, with Shaun Cummings, Calum Butcher, Jimmy Abdou and Onyedinma replacing Mahlon Romeo, Shaun Williams, Ben Thompson and Lee Gregory.
Meanwhile, Harry Donovan took his place on The Lions' bench for the first time.
Millwall's first chance came in the fifth minute, as after good work from Jed Wallace, Steve Morison's looping shot landed on the top of the Southend net.
Referee Andre Marriner waved away the appeals of The Shrimpers shortly after as Simon Cox went down under the challenge of Byron Webster inside the penalty area, with Cox dusting himself down to fire Southend's first shot of the game over the crossbar.
Fifteen minutes in, The Lions were presented with an opportunity to take the lead following Wallace's lung-busting run down the left-hand side. His original shot was saved by Ted Smith, but he received the ball back and crossed ferociously into the path of Morison, who unfortunately could not bring the ball under control and steered his shot wide.
The game was being played at a typically frenetic pace and 30 minutes in, The Lions had another chance to nudge themselves in front, however Aiden O'Brien could only fizz his shot wide of Smith's post.
The first major flash point came on 32 minutes, as The Shrimpers were reduced to ten men. Marriner showed Will Atkinson a straight red card for a crunching foul on Tony Craig halfway inside the Millwall half.
However, despite their disadvantage, the visitors rallied and could have opened the scoring five minutes before the break, but Michael Timlin sliced his shot wide whilst unmarked in the penalty area.
The controversial decisions kept coming, as The Lions had a penalty shout waved away by Marriner after Webster appeared to have been pulled down inside the six-yard box, with a frantic first-half coming to a close shortly after.
A neat passage of passing nearly set Wallace through on 54 minutes, but a combination of a bad bounce and a deflection from a Southend defender just sent the ball out of the winger's reach.
The Lions took the lead on 63 minutes. Shaun Cummings' left-footed cross found Onyedinma lurking at the back post and the front-man arched superbly to head back across goal and past the reach of Smith for his sixth goal of the campaign.
Harris freshened up the wide berths with the substitutions of Shane Ferguson and David Worrall for Wallace and O'Brien inside the final 20 minutes and it was the Northern Irishman that saved a possible equaliser on 83 minutes with a superb challenge on the edge of the penalty box.
Morison had an attempt from distance saved as a nervy final few minutes ticked their way past, with Butcher also having a shot stopped from six yards out, but Marriner blew his final whistle to a roar from the Den faithful.
The Lions are now 11 games unbeaten and enter Sky Bet League One's top six.
Millwall: Archer, Cummings, Craig, Onyedinma, Wallace (Ferguson, 70'), Butcher, Webster, Morison, O'Brien (Worrall, 82'), Cooper, Abdou. Subs not used: King, Romeo, Martin, Donovan, Smith.
Scorer: Onyedinma (63')
Southend United: Smith, Coker, Wordsworth, Thompson, Timlin (McGlashan, 78'), Cox (Nouble, 85'), Atkinson, Fortune (Robinson, 58'), Leonard, Demetriou, Ferdinand. Subs not used: Bexon, White, Amos, Inniss.
Bookings: Robinson, McGlashan
Sent off: Atkinson
Referee: A. Marriner
Attendance: 10,323 (1,381)