FULL-TIME: Swans U21s 0 Millwall U21s 1
13th April
The Under-21s suffered only their second home defeat of the season as Millwall claimed all three points at the Liberty Stadium.
The hosts had the better of the first half and came close through both Henry Jones and Kenji Gorre, while Jamie Philpot hit the woodwork for the visitors.
But Millwall improved after the interval and after a series of half chances they broke the deadlock as Noah Chesmain hit a fine shot into the top corner with 14 minutes to play.
The Swans thought they had grabbed a point late on as Stephen Fallon's effort was well saved by Tom King, but it means the hosts remain second in the table with just two games left to play.
SWANS U21s: Oliver Davies, Connor Roberts, Joe Rodon, Giancarlo Gallifuoco, Raheem Hanley, Adam King, Henry Jones (capt), Adnan Maric (Stephen Fallon, 64), James Loveridge, Kenji Gorre, James Demetriou (Owain Jones, HT)
SUBS: Gregor Zabret, Joseph Jones, Sam Evans.
MILLWALL U21s: Tom King (capt), Mahlon Romeo, Dylan Casey, Noah Chesmain, Chris Parr, James Brown, Kyron Farrell, Callum Webb (Alex Skinner, 67), Alfie Pavey, Jamie Philpot, Kris Twardek.
SUBS: Rian Bray, Seb Darton, Edere Eze, Mikael Ndjioli.
The Swans came into this fixture sitting second in the Development League Two South table with just three league games left to play, knowing victory would seem them take a big step towards the play-offs.
And they started brightly, dominating possession in the early stages as Kenji Gorre saw a shot easily saved by Millwall keeper Tom King.
But it was the visitors who nearly broke the deadlock as Dylan Casey's cross from the left was met by the head of Jamie Philpot but his deflected effort came off the top of the crossbar.
At the other end, skipper Henry Jones headed a fraction wide of the left-hand post from a fine James Loveridge cross, while Gorre was involved again late in the first period as he cut inside and saw a shot deflect inches wide of goal.
Half-time: Swans U21s 0-0 Millwall U21s
The hosts made a change at the break as James Demetriou was replaced by Owain Jones.
But it was Millwall who posed a greater threat in the early exchanges as Alfie Pavey shot wide before Oliver Davies saved well from a low drive by Noah Chesmain.
Pavey was again involved just past the hour mark as he worked some space on the edge of the box before firing over, before Davies had to be alert to keep out Jamie Philpot from close range.
Meanwhile, both sides made a change as Stephen Fallon - who scored the winner against Leeds - replaced Adnan Maric while Callum Webb made way for Alex Skinner for the visitors.
And Millwall were rewarded for their positivity by taking the lead on 76 minutes as Chesmain worked himself half a yard outside the box before hitting a superb shot past Davies into the top corner.
The Swans looked to hit back quickly as James Loveridge fired narrowly over the left-hand upright.
And the hosts thought they had grabbed an equaliser with two minutes to play as Connor Roberts pulled it back for substitute Stephen Fallon who saw a right-foot shot superbly clawed away by the outstretched hand of Tom King.