A spirited second-half display wasn't enough for Millwall's U18 side, who exited the FA Youth Cup at the hands of Reading on Thursday night.
The Royals ran out 2-1 winners at the Madejski Stadium with all three goals coming during an entertaining first-half.
Larry McAvoy and Chris Perry's side began on the front foot and almost took the lead inside 90 seconds when winger Lucas Sinclair cut in from the left before forcing Adam Desbois into a fine save with a curling effort 18 yards from goal.
The hosts looked to settle into their rhythm early on but didn't create a meaninful opening until nine minutes in when Danny Loader's driven cross into the six-yard box was turned behind by Lions skipper Jesse Debrah.
Reading should've opened the scoring moments later when Jordan Holsgrove's dangerous free-kick from the right was headed invitingly back across goal by Jack Nolan but no Royals team-mate could capitalise at the far post.
But they didn't have to wait much longer before finding the net when, on 21 minutes, Holsgrove lifted a ball over the top for Loader, who beat the offside trap before controlling in the box and slotting under Millwall keeper Sam Jackson.
The away side's best attacking work came down the left side through full-back Junior Tiensa and Sinclair, but Millwall struggled to find a way in behind Reading's defence as they searched for a leveller.
And their task became even tougher six minutes from the interval when The Royals doubled their advantage through Ayo Faniyan, who controlled Andre Burley's cross on the turn before finding the top corner from close range.
The Lions came close in response when Debrah climbed highest to meet Mason Saunders-Henry's deep free-kick, but the defender's header was tipped over by keeper Desbois and Millwall failed to make the most of the subsequent corner.
Reading couldn't see their two-goal advantage through to half-time, however, as George Alexander - son of former Millwall striker Gary - tapped home from Joe Wicks' ball into the box to halve the deficit seconds before the interval.
It didn't take long for the game to spark back to life in the second-half but it was an off-the-ball incident which was the talking point. Reading's Ethan Coleman clashed with Sinclair on the far touchline, and following a heated altercation the duo were both shown straight red cards by the referee.
It was Millwall who looked the more likely going forward and they almost drew level shortly before the hour mark when Issac Olaofe's attempted cross turned almost caught Desbois out at his near post but the Reading keeper did well to produce a vital save.
The Royals were given a golden opportunity to extend their lead, somewhat against the run of play, from the penalty spot when Debrah was harshly judged to have fouled Jamal Balogun, but keeper Jackson produced a fine stop low to his left to deny Holsgrove from the spot.
Millwall made an attack-minded double substitution after 83 minutes when Bestart Topalloj and Harry Taylor were both introduced. That move provided added impetus to their forward play and it almost paid immediate dividends when the latter was involved in a move which ended with Olaofe striking the side netting.
But despite their best efforts during six minutes of added time, The Lions were unable to find a way past a stubborn Reading rearguard, leaving The Royals celebrating their passage through to the next round.
Reading: Desbois, Burley (Elva-Fountaine, 46'), Odimayo, Holmes, Balogun, Buchanan, Faniyan (Simmo, 77'), Coleman, Loader, Holsgrove, Nolan (Wilson, 90'). Subs not used: Hillson, Lawrence
Goalscorers: Loader 21', Faniyan 39'
Sent off: Coleman 51'
Millwall: Jackson, West (Topalloj), Tiensa, Hanson, Debrah, Strachan, Olaofe, Wicks, Alexander, Saunders-Henry (Taylor, 83'), Sinclair. Subs not used: Duncan, Wright, Mitchell
Goalscorers: Alexander 45+1'
Sent off: Sinclair 51'