Millwall's hopes of gatecrashing the Play-Offs were finally extinguished as goals in either half from Darren Pratley and Steven Dobbie clinched victory for Swansea City.
It proved to be just one big game too many for The Lions, who have confounded the critics by pushing for a top six spot just 12 months after winning promotion from League One.
Having recorded maximum points from their Easter fixtures against Preston and Scunthorpe, The Lions' quite simply looked to have run out of juice at a packed Den.
Following Leeds United's win against fellow Play-Off hopefuls Burnley, and Nottingham Forest's 5-1 thumping of Scunthorpe, this was a must-win game for Kenny Jackett's side.
But the immense effort and endeavour of the previous 44 games finally took its toil as Millwall struggled against a well-drilled Swans side that, having got their goals through Pratley (30mins) and Dobbie (47mins), handed out a lesson in ball retention to frustrate The Lions.
"The better side won," said a magnanimous Jackett, "They had the livelier forwards who scored the goals and they took control.
We have had plenty of big occasions and we have risen to the challenge on numerous occasions but today we lacked energy and never really got going."
Swansea certainly enjoyed the better of a frustrating opening half, particularly from The Lions' point of view.
In tricky winger Nathan Dyer Brendan Rogers had a player who looked capable of unlocking the home defence every time he touched the ball.
It was from his mesmerising run on 18 minutes that the visitors carved out the first clear scoring opportunity of the game.
Picking up the ball on the right wing, Dyer bamboozled Scott Barron before picking out Luke Moore in space, and in a central position 18 yards out. Fortunately for Millwall the latter's rising shot flew well over David Forde's crossbar.
It was Forde who came to the rescue on 21 minutes, somehow clearing Dyer's sumptuous curling effort at full stretch by clawing the ball away for a corner.
Joe Allen sent a 25-yard fizzer wide before Swansea made the breakthrough after 30 minutes courtesy of Pratley's crisp low drive from 20 yards that flew in off the woodwork.
A disappointing opening 45 minutes for The Lions was perhaps best summed up midway through the half when James Henry overhit a corner, Steve Morison sprinted to try and retrieve it, but the ball bounced off his back and over the line for a Swansea goalkick.
Jackett made a switch at half-time bringing on Hamer Bouazza for John Marquis in a bid to get more of a grip in the middle, but within two minutes of the restart The Swans doubled their tally in somewhat fortuitous manner.
Jack Smith was laid out challenging for the ball 20 yards out, and despite clutching his head referee Mike Oliver waved play on. Dobbie proceeded to weave clear of a challenge before poking a finish high past keeper Forde and into the roof of the net.
Millwall reacted well to the goal however and twice went close to reducing the arrears.
A stinging shot by Henry was held at the second attempt by Dorius De Vries on 56 minutes and then Morison could only head the loose ball into the side-netting from close range following good work by Andros Townsend and Henry.
De Vries then had to be agile to claw out a piledriver from Tam Mkandawire from fully 25 yards before Henry sent another speculative effort over the top from way out.
However with each passing minute that saw Millwall's Play-Off dream slip further and further away, the monk chant which had started quietly grew in volume to raise the roof as the fans paid fulsome tribute to manager Kenny Jackett and the team in what has been a superb season.
The learning curve continues in SE16, and you can be sure that even though the Play-Offs are now out of reach, there is every reason to feel optimistic that the foundations are very much in place to push onwards and upwards next season.
Millwall: Forde, Smith, Barron, Trotter, Robinson, Ward, Townsend, Mkandawire (Abdou, 81mins), Morison (McQuoid, 55mins), Marquis (Bouazza 46mins), Henry. Subs not used: Mildenhall, Dunne, Craig, Purse.
Swansea City: De Vries, Williams, Taylor, Tate, Pratley, Dyer, Dobbie (Sinclair, 60mins), Moore (Borini, 66mins), Rangel, Allen, Britton (Serran, 81mins). Subs not used: Makalambay, Beattie, Orlandi, Gower.
Scorers: Pratley (30mins), Dobbie (47mins), Dobbie (47mins)
Ref: M. Oliver
Att: 15,101 (away 958)