George Alexander's 82nd-minute finish was decisive in the Professional Development League on Friday afternoon as Millwall's Under 23s defeated Sheffield United 1-0.
Alexander was in the right place at the right time to flick home Tom Elliott's knock-down and secure three more points for The Lions.
Kevin Nugent opted to bring first team squad members Luke Steele, Jason McCarthy, Shaun Hutchinson and Elliott into his starting XI, alongside the usual suspects in Jesse Debrah, Billy Mitchell and Alexander.
An uneventful first-half saw little in the way of goalmouth action, but there were a couple of chances at either end - Samuel Ompreon tried his luck for The Blades, but to no avail, whilst a combination of George Alexander, Tyler Burey and Jason McCarthy attempted to open the scoring for Millwall, but could not find a way past a resolute United defence.
With 53 minutes on the clock, Hutchinson nodded Burey's free-kick back across goal, but a combination of Debrah and Harry Ransom were unable to turn the ball home from close range.
There was a penalty shout for Millwall with 20 minutes remaining, but as Alexander tumbled inside the box, referee Mr Hughes was unmoved - Mitchell's vicious strike failed to trouble the United goal just a minute later.
Reece York then smacked the post for The Blades in what was the nearest attempt to the scoring being opened, before Illiman Ndiaye then forced Steele to tip behind as United pushed forward.
With eight minutes remaining, The Lions took the lead. After a succession of corner-kicks, Reuben Duncan's cross found the head of Elliott, and after he nodded towards goal, Alexander was there to steer home from close range.
United attempted to get back into the game late on, but Millwall held firm to claim victory.
Millwall: Steele, McCarthy, Tiensia (Moss 46'), Hutchinson, Debrah, Ransom, Burey, Mitchell, Elliott (Bradbury 90+1'), Alexander, Duncan. Subs not used: Fanshawe, Strachan, Munting.
Scorer: Alexander 82'
Sheffield United: Amissah, Sheppeard (J. Kelly 77'), Mallon, Hall, Gomis, Ferguson, Hoti (Andall-Gibbons 68'), Ndiaye, Young, Ompreon, York. Subs not used: Neal, S. Kelly, Ackroyd.
Referee: Mr. S. Hughes