Millwall striker Josh Coburn came off the bench to score his second Championship goal of the season as the Lions beat promotion rivals Watford at Vicarage Road.
Top scorer Femi Azeez gave the visitors the lead in the 69th minute having had the better chances in a goalless first half.
Coburn, who returned from a long injury lay-off to score against Burnley in the FA Cup last weekend, ran through one-on-one before finishing in the bottom corner to double Millwall’s lead with nine minutes remaining.
The game threatened to boil over as tempers flared from both sides but, on his 50th match in charge of Millwall, Alex Neil’s side saw out a win that lifted them up to fourth in the table before Preston’s game with Derby.
The Lions are now unbeaten in five league matches following a difficult period before Christmas, while defeat ends a run of four straight Championship victories for Watford.
This was Watford’s first defeat at Vicarage Road since September and just their second at home in the Championship this season.
Millwall were the much better side in a goalless first half, with Alfie Doughty coming closest for the visitors when he smashed an effort just over the bar.
There was confusion among both sets of players and officials when a ballboy ran onto the pitch and prevented a wild Casper De Norre shot from going out for a throw in, with referee Ruebyn Ricardo eventually awarding a drop ball in the corner, which resulted in a Watford goal-kick.
It took until the seventh minute of first-half added time for Watford to register their first shot – a James Abankwah header that drifted just wide of Max Crocombe’s post.
The Hornets were much improved after the break, pressing higher up the pitch. But it was Millwall’s half-time substitute Macaulay Langstaff who should have made the breakthrough, heading over Azeez’s excellent cross from point-blank range.
The Watford defence somehow managed to scrape the ball away after Tristan Crama had got beyond goalkeeper Egil Selvik from a Millwall corner, before opposite number Crocombe made smart stops from Marc Bola and Tom Ince.
Millwall finally made the breakthrough on 69 minutes, with Crama flicking Doughty’s high cross down to Azeez, who slotted the ball along the turf and into the back of the net.
The second put the visitors in total control, as the Lions turned the ball over in midfield and Camiel Neghli played a pinpoint pass for Coburn to chase and finish.
The former Middlesbrough striker has now scored two in two since returning from a quad injury sustained in October and gives Millwall boss Neil a much needed boost to his frontline.
Watford boss Javi Gracia said: “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 boss Alex Neil said: “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.”
