Millwall moved to within two points of the play-off places with a 1-0 win at relegation-threatened Reading.
The Lions edged ahead in the 37th minute when defender Jake Cooper nodded home unmarked from a corner.
Although Reading dominated after the interval, Millwall held strong to secure a fifth successive league victory.
The Londoners sat five points off a top-six berth prior to kick-off and they started brightly as Reading opted to sit back and absorb the pressure.
Jed Wallace wasted a good chance from a free-kick on the edge of the home area, ballooning the ball over the crossbar.
Reading responded quickly with Tom Ince trying his luck from 20 yards, but Millwall goalkeeper Bartosz Bialkowski was equal to it and made an agile save.
Ince had another attempt after cutting in from the right, but Bialkowski was again well positioned to make the stop.
Millwall regained the initiative, with Cooper heading wide from a deep Danny McNamara cross.
Reading goalkeeper Luke Southwood then made a superb stop to tip over a fierce 20-yard effort from McNamara.
But from Wallace's corner in the 37th minute, former Reading centre-back Cooper nodded home unchallenged at the far post.
The hosts reacted positively before the break, with midfielder John Swift presented with two opportunities. First he shot over the crossbar after a one-two with Lucas Joao, then Bialkowski touched away his precise free-kick.
Reading created the first chance of the second period, with Joao finding space in the Millwall area. The forward took too long to control the ball and was quickly hounded out of possession.
Ince then saw a drive deflected wide and, from Swift's corner, Joao was unable to keep his header on target.
Millwall offered little going forward, appearing to be satisfied just to hold onto their 1-0 lead.
But their defence was extremely well marshalled, with Cooper particularly dominant in the air.
When Millwall did manage to break, after a swift passing move that flowed from right to left across the pitch, Scott Malone saw his final effort blocked.
Reading again upped the tempo in the closing stages but the visitors comfortably repelled all that they could offer.
What the managers said...
Reading's first-team coach Michael Gilkes: "Yes, we had plenty of the ball, but we lacked that little bit of quality in the last third. From a performance point of view, I think it was really positive. But we struggled to break down Millwall in the most crucial part, which is in their goal.
"One of Millwall's strengths is their set-pieces. They had seven opportunities today and six of them were from set-pieces. They had one shot that led to the corner that then led to the goal. They are extremely good at that. Cooper is a threat in both boxes, as we knew, and we had prepared as best we could. But that was the difference today."
Millwall's Gary Rowett: "It was a good delivery from Jed Wallace and Jake rises highest against his old club. It was a great header and he's scored a few of them in recent weeks. He's been invaluable to us.
"I thought he was excellent today. As our captain, he gave a real leadership performance. And to cap it all with a goal that wins us the game was really nice."