Cardiff City slumped to their third defeat in four games courtesy of second-half goals from Millwall's Charlie Cresswell and Benik Afobe.
By Glen Williams
The Lions dominated much of the game, but Cardiff arguably had the best chances, with both Sheyi Ojo and Mark Harris hitting the post in each half.
But the Lions goal always looked like it was coming and it was Cresswell who put the hosts in front with a commanding header before Afobe finished off a wonderful mazy run with a cool finish past Ryan Allsop.
A disappointing afternoon which City simply have to put behind them if they are to start a climb back up that table any time soon.
The main talking point before the game was the decision by Steve Morison to start new signing Callum Robinson on the bench.
The manager has staunchly backed Max Watters, for the most part, this season and gave him yet another chance to prove his worth in front of goal.
There was no place in the squad, however, for Rubin Colwill or Callum O'Dowda, who missed the last game through injury following a hip issue he sustained against Preston North End.
Tom Sang was a notable name on the bench, preferred to Joel Bagan as that replacement full-back option.
When the game got underway, Millwall were the ones on the front foot, pinning City back for large periods as the visitors struggled to make any sort of impact.
The first meaningful chance of the match, however, did fall Cardiff's way thanks to Watters, who, on the quarter-of-an-hour mark, hooked a lovely ball into the box and Jaden Philogene raced on to it, sending a header towards the far corner. It was just wide, though.
It would have been completely against the run of play, however, because the Lions were dominant. Cardiff could barely get out of their own half and were suffocated for much of the early exchanges.
Zian Flemming went very close with a cultured, left-footed effort from just inside City's box, but Ryan Allsop watched it sail just past his right-hand upright.
Callum Styles was a thorn in City's side, too, particularly Mahlon Romeo, who was met with raucous boos every time he touched the ball. He beat the Bluebirds right back during one marauding run and squared a pass into the path of Andreas Voglsammer, who only had to tap it home from eight yards out, but his connection was poor and the shot was sent wide.
It looked inevitable, actually, that Cardiff would concede before the break, but somewhat against the run of play, a rare Bluebirds counter-attack saw Niels Nkounkou brilliantly fashion himself some space before sliding an excellent cross across the face of goal. Sheyi Ojo was the man on the end of it, poking a shot towards goal, but his effort pinged back off the post and away from danger. It was the best chance of the half by a country mile for Cardiff, who went into the break needing a huge regroup.
Morison saw fit to introduce debutant Callum Robinson and Mark Harris at half-time, with City's attack needing some impetus.
Robinson looked bright after his introduction, while Harris almost gave City the lead. The Welshman pinged a low shot from the edge of the box and it cannoned into the far post. The second time Cardiff hit the woodwork.
And it was twice as painful, too, because Millwall went straight up the other end to score. An outswinging corner was met by the rising Charlie Cresswell, who buried his header after outjumping Perry Ng to put the Lions ahead.
The game was stretched from then on as Cardiff pushed to level the scores and it presented chances at both ends. The best of which came for Nkounkou, who did fantastically well to skin his man and drive into Millwall's box before unleashing a clever right-footed effort. Bartosz Bialkowski did well to deny him, though.
In truth, barring two efforts against the run of play which hit the woodwork, Cardiff were second best all afternoon and could have few complaints about the result. When Afobe beat Nkounkou down the left late on and slammed the ball into the roof of the net, it was no less that Millwall deserved.
It means Cardiff are now five games without a win and desperately need it all to click into gear quickly.
Millwall XI: Bialkowski; Hutchinson (Cresswell 48), Cooper, Wallace; Styles, Saville (Malone 62), Mitchell, Shackleton; Voglsammer (Burey 62), Flemming (Honeyman 90); Bradshaw (Afobe 62).
Subs: Long, McNamara.
Cardiff City XI: Allsop; Romeo, Ng, Kipre, Nkounkou; Wintle, Rinomhota, Sawyers (Whyte 68); Philogene (Ralls 68), Watters (Robinson 45), Ojo (Harris 45).
Subs: Alnwick, Sang, Simpson.
You do not have the required permissions to view the files attached to this post.