Benik Afobe's double helped Millwall end Huddersfield's 17-match unbeaten league run with a deserved victory at the New Den.
The visitors would have gone level on points with second-placed Bournemouth with victory, but they were undone by a goal in each half from Afobe.
The on-loan Stoke forward also hit the bar and the post as the hosts dominated proceedings.
It is now eight games unbeaten for the Lions, a run which has taken them to 10th place and within two points of the play-offs.
Huddersfield had begun full of confidence and had four attempts in the first 10 minutes, with goalkeeper Bartosz Bialkowski saving well from Lewis O'Brien and Duane Holmes.
But Millwall withstood that pressure before growing into the game, and Afobe would have put them ahead but for a fine goal-saving tackle from Matty Pearson on his 400th career appearance.
However, the striker made amends with a fine finish for his first goal in seven games - and 50th in the Championship - as Terriers skipper Jonathan Hogg was punished for carelessly giving away possession in midfield.
Afobe's second arrived early in the second half as Huddersfield failed to deal with Scott Malone's free-kick and the frontman hit it first time on the volley from just inside the area.
There was no response from Carlos Corberan's side who were lucky not to suffer a heavier defeat.
Afobe hit the bar, the post and was denied by goalkeeper Lee Nicholls as Millwall edged closer to sixth-placed QPR, having also kept five successive clean sheets.
Millwall manager Gary Rowett told BBC London 94.9:
"I thought we were excellent again and the three points were deservedly ours.
"Bart had to make a couple of saves early on. but after that on the balance of attacks, most of the game was ours.
"We were really incisive on the break and our front three caused them lots of problems."
Huddersfield Town head coach Carlos Corberan told BBC Radio Leeds:
"We came here with the idea to show the performance that we can show, but during the game, we couldn't find the best of our style in attack.
"At no moment did we break the last line of their defence and we lost more balls in the middle of the pitch than we usually do.
"When you start to lose balls without pressure, you give opportunities to the opponent to counter-attack and that's what happened with their first goal."