Millwall's Under 23s were defeated 2-1 by Cardiff City in the Professional Development League on Monday afternoon.
After a goalless first-half, Tom Sang and James Waite moved The Bluebirds into a two-goal lead. Jayden Davis pulled one back for Kevin Nugent's men with 17 minutes remaining, but The Lions were unable to find the equalising goal, instead slipping to defeat.
Billy Mitchell curled an early effort wide for Millwall at the Cardiff International Sports Campus, before Ryan Sandford had to be at his best to deny Waite as the first 45 minutes came to a close.
Omar Bogle then had an effort saved by Sandford, but the hosts were in front just six minutes later after Sang turned home Jacob Evans' cross.
With 20 minutes remaining, Waite doubled Cardiff's lead courtesy of a shot from the edge of the area. Nugent's side halved the deficit on 73 minutes through Davis, tapping home from close range, but despite late pressure, could not level the scoreline.
Next up for Millwall's Under 23s is a date at The Den with Coventry City on Thursday - and you can view ticket details here.
Millwall: Sandford, Moss, Tiensia, B. Mitchell, Topalloj, Strachan, Burey (Olaofe 60'), Skeffington (Muller 72'), Alexander, Duncan, Davis. Subs not used: Wright, O'Brien, A. Mitchell.