Albion will need to beat Charlton in their final group game and hope other results go their way if they are to progress in the EFL Trophy after losing their second Group G contest at Crawley Town's People’s Pension Stadium.
AFC Wimbledon secured their second group win thanks to a first-half header from Zach Robinson and a late penalty by Adam Roscrow.
The Seagulls had their moments and dominated possession for spells in the second half, but Wimbledon restricted them to very few clear sights of goal with Jensen Weir missing their best chance when he blasted over from 15 yards.
Wimbledon got on top early on and went in front after 20 minutes. Paul Osew got the better of Sam Packham on the left and his chip to the far post was headed powerfully down and past Carl Rushworth by Robinson.
As the hosts probed for a second, Will Nightingale headed just over and Rushworth blocked a shot from Roscrow, who then glanced a header from a corner against the bar.
But Simon Rusk’s teams have a habit of staying in games even when they are not quite at their best and just before the break they began to threaten with Packham’s low cross in the 40th minute touched goalwards by Danny Cashman who forced a smart low save out of Dons keeper Nik Tsanev.
Substitute Ed Turns went close to turning in Weir’s free kick to the far post early in the second half as Albion began to dominate possession. Weir had Albion’s best chance in the 74th minute after substitute Jack Spong found him 15 yards out but his right-foot shot went well over. At the other end, Roscrow headed just wide.
With five minutes to go Spong brought down Ethan Chislett and the referee awarded a penalty which Roscrow powered past Rushworth to seal Wimbledon’s victory.
Ulrick gets his chance...
Ulrick Eneme Ella, the 19-year-old French striker who completed his move to Albion earlier in the day, made his debut with 25 minutes to go and certainly gave the attack a different dimension with his physicality, although he didn’t have too many opportunities to show what he can offer.
With some of the youngsters expected to be involved in Wednesday’s Carabao Cup tie at Preston, there were five changes to the under-23 team that drew 2-2 against Arsenal on Friday. Among those coming in was Tudor Baluta, the Romanian who has spent last season at loan at his former club Viitorul Constanta.
Wimbledon were similarly youthful, with only Alex Woodyard surviving from the team which shared eight goals with Plymouth in League One on Saturday. Albion striker Ryan Longman, who scored for the Dons in that game, wasn’t involved against his parent club.
Albion: Rushworth, Baluta (Turns 45), Tsoungui, Packham, Furlong, Leonard (Spong 61), Crofts, Weir, Vukoje, Cashman, Wilson (Ella 65).
Subs not used: Desbois, Tanimowo, Everitt, Collyer.
Albion under-23s take on Chelsea in Premier League 2 on Friday, kick off 7pm.