*Lions beaten 8-7 on penalties
Millwall's U21 Development Squad exited the League Cup after losing 8-7 to West Ham United U21s on penalties following a 1-1 draw after extra-time.
Fred Onyedinma looked to have won it for The Lions in extra-time but Hammers substitute Jaanai Gordon scored an immediate equaliser to send the tie to penalties, which the hosts won when Dylan Casey's effort was saved.
The home side produced the first meaningful attack of the game but Matthias Fanimo's cross into the box was turned away by Jake Goodman at the near post.
Just seconds later Hammers midfielder Manny Onariase had the ball in the net only to see the linesman put his flag up for an offside earlier in the move.
Millwall's first chance of the game fell to Jack Powell, but the midfielder could only send a powerful effort from 25-yards over the bar before doing the same with a free-kick minutes later.
Neil Harris' side were enjoying the better of the opening exchanges with Powell and Ben Thompson controlling the midfield, and it was the latter who had The Lions' next chance, firing an effort just wide after positive play from Fred Onyedinma down the right.
Keeper Tom King found Aiden O'Brien with a long ball forward in the 18th minute, but the Irish striker, playing the lone frontman role in a 4-2-3-1 formation, could only head into the arms of West Ham keeper Sam Howes.
The best chance of the game up to that point, though, fell to Thompson, though the midfielder could only fire wide after bursting into the box.
Just two minutes later Onyedinma latched onto a through ball to go one-on-one with keeper Howes, who produced a smart save to deny the forward and keep the scores level at half-time.
Onyedinma was involved in the first key moment of the second-half, racing onto Powell's pass and beating his marker, Onariase, who brought him to ground and picked up a yellow card.
The Lions continued to control large parts of the game but were dealt a blow when midfielder Sofiane El Bekri was stretchered off in the 63rd minute with what looked like an ankle injury to be replaced by striker Alfie Pavey.
West Ham's first meaningful opportunity of the second-half fell to Kieran Sadlier, who headed Bywater's cross over the bar.
With extra-time beckoning, and the game becoming increasingly stretched as both sides searched for a winner, Sid Nelson and then Onyedinma both missed opportunities to score; the defender firing over after a corner and the forward hitting the side netting with a far post header.
Harris added fresh legs to his midfield for the extra period, replacing Thompson with Callum Webb, and it helped to further his team's control of proceedings as they continued to restrict the home side to few goalscoring opportunities.
With the game heading towards penalties, The Lions deservedly opened the scoring when Powell fed the lively Onyedinma, who took a touch before slotting past Howes.
West Ham, who hadn't looked like scoring during extra-time, were sparked into life and found an immediate equaliser when substitute Jaanai Gordon headed past King to ensure that penalties would decide the winner.
The two teams scored 15 consecutive spot-kicks before left-back Casey, on as a second-half substitute, saw his effort saved by Howes to seal the hosts' progress to the next round of the League Cup.
Millwall: King; Siafa, Nelson, Goodman, Wood (Casey, 72'); Powell, Thompson (Webb, 91'); Onyedinma, El Bekri (Pavey, 63'), Jeffrey; O'Brien. Subs: Girling, Twardek