Albion exited the Emirates FA Cup following a battling 3-1 extra-time defeat to Brighton & Hove Albion in their fourth-round replay at The Hawthorns.
Seagulls substitute Glenn Murray converted twice in additional time to settle the encounter and set up a fifth-round meeting against Derby County.
Kyle Bartley had put the Baggies in front in unusual fashion in the 77th minute, hooking the ball home into the net while standing on the byline the other side of a post.
Yet Premier League Brighton levelled late on courtesy of Florin Andone, who capitalised on a defensive misunderstanding, to send the tie into extra time.
Defeat was tough on a much-changed Baggies side, which included four Academy graduates for a large part of the tie - Sam Field, Rekeem Harper, Rayhaan Tulloch and debutant Morgan Rogers - and also played the last 20 minutes with 10 men due to injury to Hal Robson-Kanu.
Robson-Kanu had earlier sent a volley against the crossbar while Leon Balogun also headed against the woodwork for the visitors.
There's little time to dwell for Albion as they prepare to travel to Stoke City in the Sky Bet Championship this weekend.
The Baggies made seven changes from Saturday, mirroring a similar line-up to the initial meeting against Brighton, with captain Jake Livermore and frontman Jay Rodriguez coming into the starting XI from the goalless first encounter at the Amex Stadium.
Albion started positively and Rodriguez stung the palms of David Button after just eight minutes before again testing the Seagulls stopper from long range shortly afterwards.
Yves Bissouma was first to trouble Jonathan Bond from distance as both sides went on to enjoy further half chances in a lively opening quarter.
Field was on the end of an elbow from Andone which went unpunished, before the visitors enjoyed three good chances in a matter of as many minutes.
Firstly, Bond saved well from Anthony Knockaert before Balogun headed against the crossbar from a subsequent corner, with Andone then dragging an opening across the face of goal.
Yet Albion hit back just before the break and Robson-Kanu himself sent an expertly-taken 20-yard volley against the crossbar, with the tie goalless at the interval.
Craig Dawson came on for Rodriguez at half-time, with the Baggies switching their system.
Bond was called upon to save well from Alireza Jahanbakhsh while Harper fired wide at the other end.
Bissouma sent a chance off target, Field doing likewise as Academy graduate Tulloch, 18, replaced Livermore for his maiden appearance at The Hawthorns.
Dan Burn headed wide from a corner for the visitors before the Baggies finally broke the deadlock.
Hoolahan's inswinging free-kick was headed upwards in the six-yard area and Bartley, standing on the byline the other side of the far post, hooked his leg around to convert.
Tulloch headed narrowly wide before the Seagulls pounced on a defensive mix-up to level matters in the 82nd minute courtesy of Andone's low finish past Bond.
Rogers, at just 16 years of age, was introduced for his senior debut as the tie hung firmly in the balance.
And Robson-Kanu's sweeping effort off target in the closing stages ensured extra-time.
Ahmed Hegazi replaced sub Dawson, with each side allowed a fourth substitution in the additional 30 minutes, although the hosts lost Robson-Kanu to injury in the 99th minute, ensuring they played the remainder of the tie with 10 men.
And from there, Murray scored twice to inflict defeat on a resilient and hard-working Albion and seal Brighton's progress into the fifth round.
Albion: Bond, Mears, Bartley, Adarabioyo, Townsend, Harper, Livermore (c) (Tulloch 63), Field, Robson-Kanu, Hoolahan (Rogers 82), Rodriguez (Dawson 46, Hegazi 91).
Subs: Myhill, Gibbs, Gayle.