Harry Cornick did well to sort his feet before a composed finish for his second goal
Harry Cornick scored in each half as a clinical Luton Town inflicted a first Championship defeat in eight games on Millwall.
With the away side's first real chance, an unmarked Cornick bent the ball into the top corner first time from 14 yards after a determined run and pass from Jordan Clark.
Millwall then huffed and puffed without creating any clear openings, Benik Afobe and Sheyi Ojo having efforts blocked with the hosts struggling in the final third.
Clark again released Cornick for Luton's second, the forward shooting low across goal and into the corner, and the Lions' day was summed up late on when Jed Wallace saw a decent penalty excellently saved by Sluga.
Victory extends 10th-placed Luton's unbeaten run to three, all without conceding, while Gary Rowett's Millwall drop below their opponents, into 14th, after a first league loss since 21 August.
- Relive Saturday's EFL action as it happened
There was a lively atmosphere inside The Den at kick-off but the hope side failed to feed off that, falling behind when Jake Cooper's poor header under pressure allowed Luton to ruthlessly pounce for their opener.
Cornick, 26, scored just once in 43 appearances for Luton last season but grabbed his sixth of this campaign - and second brace in three matches - with a composed finish after the Hatters came out on top in a midfield battle.
The recalled Pelly Ruddock Mpanzu rattled the bar from 25 yards as Nathan Jones' side threatened to run riot while, after Cornick was withdrawn in the 68th minute, Millwall did everything but score.
Wallace saw a fine free-kick tipped away by Sluga before also being denied from the spot by the Croatia keeper after Kal Naismith had handballed in the box.
But it was not to be the Lions' day as they suffered their first defeat in 10 against Luton, who avoided defeat in London for the first time in 10 league visits to the capital.
- Line-upsMatch StatsLive Text
Line-upsMillwall
Formation 3-4-2-1
33Bialkowski26Ballard4Hutchinson5Cooper2McNamara28Evans17Saville3M Wallace7J Wallace14Ojo23Afobe
- 33Bialkowski26Ballard4Hutchinson5CooperBooked at 69mins2McNamaraSubstituted forSmithat 55'minutes28EvansSubstituted forMitchellat 78'minutes17Saville3M WallaceSubstituted forLeonardat 67'minutes7J Wallace14Ojo23AfobeSubstituted forBennettat 78'minutes
Substitutes
- 1Long6Kieftenbeld9Bradshaw10Smith18Leonard20Bennett24Mitchell
Luton
Formation 3-4-1-2
12Sluga15Lockyer5Bradley4Naismith2Bree6Rea17Mpanzu29Bell18Clark11Adebayo7Cornick
- 12Sluga15LockyerSubstituted forBurkeat 87'minutes5Bradley4NaismithBooked at 83mins2BreeBooked at 84mins6Rea17Mpanzu29Bell18ClarkBooked at 72minsSubstituted forLansburyat 76'minutes11AdebayoSubstituted forMuskweat 79'minutes7CornickSubstituted forJeromeat 68'minutes
Substitutes
- 1Shea8Berry16Burke23Lansbury24Onyedinma26Muskwe35Jerome
Referee:Chris KavanaghAttendance:14,227Match StatsHome TeamMillwallAway TeamLutonPossessionHome58%Away42%ShotsHome14Away6Shots on TargetHome5Away2CornersHome12Away3FoulsHome10Away18Live TextPost update
Match ends, Millwall 0, Luton Town 2.
90'+5'Full Time
Second Half ends, Millwall 0, Luton Town 2.
90'+4'Post update
Attempt saved. Matt Smith (Millwall) header from the centre of the box is saved in the top centre of the goal. Assisted by Jed Wallace with a cross.
90'+3'Post update
Attempt missed. Jake Cooper (Millwall) header from the centre of the box is too high. Assisted by Jed Wallace with a cross following a corner.
90'+2'Post update
Corner, Millwall. Conceded by Kal Naismith.
90'Post update
Danny Ballard (Millwall) wins a free kick in the defensive half.
90'Post update
Foul by Cameron Jerome (Luton Town).
89'Post update
Foul by Ryan Leonard (Millwall).
89'Post update
Amari'i Bell (Luton Town) wins a free kick in the defensive half.
87'Substitution
Substitution, Luton Town. Reece Burke replaces Tom Lockyer.
87'Post update
Foul by Mason Bennett (Millwall).
87'Post update
Admiral Muskwe (Luton Town) wins a free kick in the defensive half.
85'Post update
Corner, Millwall. Conceded by Sonny Bradley.
85'Post update
Corner, Millwall. Conceded by Cameron Jerome.
84'Booking
James Bree (Luton Town) is shown the yellow card.
84'Post update
Corner, Millwall. Conceded by Kal Naismith.
84'Post update
Penalty saved! Jed Wallace (Millwall) fails to capitalise on this great opportunity, right footed shot saved in the bottom left corner.
83'Booking
Kal Naismith (Luton Town) is shown the yellow card for hand ball.
82'Post update
Penalty conceded by Kal Naismith (Luton Town) with a hand ball in the penalty area.
81'Post update
Corner, Millwall. Conceded by Kal Naismith.
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Source: bbc.com