Femi Azeez returned to the club which once released him to inspire Millwall to a 2-0 victory over promotion rivals Watford at Vicarage Road.
Goals from Azeez, a Watford youth product until he was let go at the age of 14, and Josh Coburn kept Millwall in the play-off positions and brought a shuddering halt to Watford's four-game winning run in the Championship.
It was a contest which became increasingly tetchy as the game wore on with players squaring up to each other a number of times in the second half.
That was in contrast to a largely uneventful first period after Watford goalkeeper Egil Selvik produced an acrobatic save to tip over an early Caleb Taylor header.
A stop-start game was being delayed by numerous injuries and an incident when a ball-boy entered the playing area and caught the ball in the mistaken belief that the ball had curled out of play.
Visitors Millwall had the most impressive player on show in the first half in Azeez. The winger frequently skipped his way past defenders and fired a rising shot just over after 24 minutes.
The game became increasingly fractious as half-time approached with over-fussy referee Ruebyn Ricardo only adding to the lack of rhythm with some bizarre decisions.
While free-flowing football was in scarce supply, opportunities kept cropping up.
Having dragged an earlier shot wide, Alfie Doughty wasted an even better chance four minutes before half-time, lashing his shot from an angle wildly over the bar.
Watford offered little, although they might have taken the lead on the stroke of the interval when James Abankwah headed wide from a Tom Ince corner.
The general flow of the game towards the home goal continued into the second half when substitute Macaulay Langstaff threw himself at an Azeez cross and watched as his header flew wide.
Watford simply could not find the rhythm which had lifted them into the promotion play-off places with four successive Championship victories in a seven-game unbeaten run.
Manager Javi Gracia tried to change that with a double substitution after 65 minutes. As part of that tactical play, Ince was switched to the right flank and immediately began a move which ended with Marc Bola shooting into the side netting from a Giorgi Chakvetadze pass.
The false hope created by that chance was extinguished almost immediately when Azeez put Millwall in front.
Doughty fought to keep the ball in play, then sent over a cross which eventually found Azeez who shifted the ball to his right before firing home a low shot.
Substitute Coburn then confirmed Millwall's victory in the 81st minute when he slid the ball home after racing onto a clever Camiel Neghli pass.
Watford's Javi Gracia:
"It's obvious this wasn't our best game. We knew that Millwall are really strong, but we didn't do our job. We tried to find a way to progress and play in our style, but we didn't do it.
"When we conceded the first goal after a mistake it was difficult for us to control the game. Millwall deserved their reward.
"When it came to showing our quality one-on-one or finishing with composure today was not our day.
"I'm frustrated, the players are frustrated, our fans are frustrated. We suffered today because Millwall were strong, but they did their job. We knew that before the game.
"We have to learn that when games are so tight and close, we have to be ready. to defend and attack in small spaces."
Millwall's Alex Neil:
"At this stage of the season, winning is obviously the most important thing, but how you win does matter.
"In the first half we were very dominant and they couldn't get out of their half much.
"We talk a lot about doing the hard yards and sometimes at this level you can beat teams through persistence and put the effort in that maybe other teams won't.
"So I was delighted with the lads. I thought we showed real hunger, real desire and I thought that we deservedly won the game."
