A youthful Albion side were beaten 5-1 by Brentford in the PL Cup on Monday evening.
Noah DuPont's first-half header was not enough for Leigh Downing's side, which included a number of U18 players, as they fell to their first defeat in the competition in the capital.
The game started in a quick fashion, with DuPont putting the Baggies into the lead with a wonderful header on the ten-minute mark.
The visitors' lead could have doubled just a matter of minutes later, but for a smart Reginald Rose save denying a surging Deago Nelson.
The hosts pressed Downing's side in hope of a first-half equaliser, and it came in the 37th minute through Michel Boni.
Brentford had their tails up, and the second came less than two minutes later as Iwan Morgan broke free and slotted past Louis Brady from close range.
The hosts got a third ahead of the break, with Morgan striking a deflected effort into the back of the net to leave the Baggies with a mountain to climb in the second half.
That mountain got bigger just seven minutes into the second period as Boni grabbed his second after finding the back of the net from close range.
Kevin Mfuamba fizzed an effort past the post as Albion tried to find a route back into the game, and DuPont also saw a bouncing headed effort tipped over the bar.
Miller McDonald was next to threaten the Bees' goal, first striking the bar with a header before his follow-up flew just wide.
A fifth came harshly against the Baggies, as Kyrie Pierre took aim from distance, only for his effort to deflect and leave Brady with no chance and cap off a clinical evening for Brentford.
The result leaves Albion second in their group, behind the Bees, with seven points from their four games so far.
Albion: Brady (GK), Nelson, Mohammed, Humpries (c), Dupont (Perkins 72'), Parker (Maughan 58'), Colesy, Mfuamba (Gombe 72'), Iddrisa, Okorodudu (McNeil 58'), Ntege (McDonald 58')
Subs not used: None.
(Photos provided by Pro Sports Images)