Millwall suffered a first home defeat of the season on Saturday afternoon as Huddersfield Town were 3-0 winners at The Den.
Josh Koroma gave The Terriers a first-half lead, before Pipa's shot crept over the line a minute from time to secure the game. Lewis O'Brien then added the gloss in injury-time.
Two changes were made to the starting XI which defeated Preston North End 2-0 on Wednesday night, as Tom Bradshaw stepped up to replace the injured Kenneth Zohore and Connor Mahoney came in for Mason Bennett. Jiri Skalak, meanwhile, was named on the bench.
The Lions were denied what appeared to be a blatant penalty-kick with just four minutes on the clock after Jake Cooper was hauled to the floor following a free-kick, but Gavin Ward was unmoved. The man-handling in the box continued just a minute later as this time Shaun Hutchinson hit the deck, with Naby Sarr having to head away from underneath his own post from a corner-kick as the lively start continued.
The first 10 minutes went on with Huddersfield struggling to escape their own half, but The Terriers benefited from a lucky bounce to allow Josh Koroma a run on goal - Cooper, however, was able to block his shot.
The visitors were unable to cope with Millwall's high press, with The Lions forcing numerous defensive mistakes from Huddersfield, but after five corners were forced within the first 15 minutes of the game, the score remained goalless. Koroma then tried his luck from outside the area at the other end, but Bartosz Bialkowski comfortably saved.
On his 50th appearance, Mahoney beat his man and crossed with 17 minutes on the clock, but Scott Malone's header was weak and gathered by Ben Hamer. However, at the third attempt, Koroma was able to open the scoring as his deflected effort scrambled into the bottom corner.
Murray Wallace had to block from the goalscorer shortly after as Huddersfield went in search of a second goal, and with the game becoming more of a midfield battle from there, the next action in front of goal came two minutes before the break, but Bradshaw's through-ball could not be utilised by Mahlon Romeo. Malone's cross then found Mahoney, but Hamer stretched to tip his low, goal-bound effort behind.
Matt Smith was brought on for Bradshaw at the half-time break, with the first action of the second-half taking place in front of the Huddersfield goal as Ryan Leonard's deflected effort flew up into the hands of Hamer.
The Lions began the second-half how they started the first - forcing a succession of corners - but were unable to break down a resolute Huddersfield defence. Leonard and Smith were the next pair to have a go at goal, but neither could find the back of the net. Jed Wallace then looked to pick out the top corner from distance, but sent his attempt wide.
At the other end, The Terriers were dangerous on the break and could have had a second on the hour-mark, but Isaac Mbenza's shot curled just past Bialkowski's far post. Adama Diakhaby then struck from distance, but again, fortunately for Millwall, the ball whistled past the post.
Koroma tested Bialkowski as the last 15 minutes of the afternoon came into view, with the same combination again sprung into action one minute later as a loose ball bounced around the Millwall penalty area.
Cooper struck wide from distance before Romeo's cross was gathered on the line by Hamer, but a second goal of the game looked like being Huddersfield's as substitute Pipa cut inside - his effort, though, went just over the crossbar.
Smith's knockdown found another substitute, Jon Dadi Bodvarsson, with two minutes remaining, but the Icelander's shot was blocked - and that proved to be fatal, as The Terriers broke away up the other end and found a way to goal - just - as Pipa's shot crept over the line despite Bialkowski's parry into the air.
As The Lions chased the game, O'Brien latched on to Leandro Bacuna's pass to guide an effort home into the net.
Millwall: Bialkowski, M. Wallace, Hutchinson, Cooper, J. Wallace, Bradshaw (Smith 46'), Romeo, Malone (Bennett 64'), Leonard, Woods, Mahoney (Bodvarsson 79'). Subs not used: Fielding, Thompson, Ferguson, Skalak.
Huddersfield Town: Hamer, Toffolo, Hogg, O'Brien, Pritchard (Bacuna 46'), Diakhaby (Pipa 67'), Duhaney, Mbenza (Campbell 85'), Koroma, Sarr, Schindler. Subs not used: Pereira, Stearman, Eiting, Brown.
Scorer: Koroma 18', Pipa 89', O'Brien 90+3'
Referee: Gavin Ward