ALBION succumbed a 3-1 defeat at Stoke City despite a dominant second-half rally at the bet365 Stadium.
First-half goals from Joe Allen and Maxim Choupo-Moting, in injury time, put the Potters in control at the break in what was the 100th top-flight meeting between the two sides.
Salomon Rondon slotted Albion back into contention early in the second period, marking his 100th game for the club with a deserved goal.
The Baggies then applied a host of second-half pressure in search of a leveller, dominating proceedings, but City's Ramadan Sobhi hit a decisive third in added time to secure the points.
Albion, who will also have to check on an injury to the returning Nacer Chadli, face Everton at The Hawthorns next up on Boxing Day as they strive to get back on track.
Head Coach Alan Pardew made three changes from the defeat to Manchester United, recalling Chris Brunt, Gareth Barry and Hal Robson-Kanu while there were places on the bench for fit-again pair Chadli and Craig Dawson.
James McClean and former Baggies skipper Darren Fletcher exchanged early efforts on target, before Rondon fired over the crossbar amid a lively start.
Yet it was the Potters who struck first in the 19th minute, Allen poking home from close range after Ahmed Hegazi's block had fallen kindly into the path of Peter Crouch and he volleyed across the face of goal.
Rondon tested Jack Butland with a low effort shortly after, and having then rode a spell of home pressure, the Albion No.9 fired a clear-cut chance over the bar when in space 12 yards out although the assistant raised his flag for offside.
It was Rondon again who was at the heart of the action just before the interval, seeing his low side-footed strike tipped around a post by Butland.
With half-time looming, Pardew's side found themselves two goals down as Allen latched on to a throw-in down Albion's left, sent clear Choupo-Moting, who rounded Ben Foster and slotted home past Hegazi and Allan Nyom.
Chadli was introduced at the break and Albion rallied with an immediate response, Rondon latching on to Brunt's ball over the top to slot past Butland in front of a sell-out 2,300 away support.
Chadli's return lasted just 15 minutes as he hobbled off with what appeared to be a thigh muscle injury on the hour mark, to be replaced by Jay Rodriguez.
Nevertheless, Albion's spell of pressure became sustained as Jake Livermore volleyed an effort wide, Brunt went close through a sucession of corners while Rodriguez was inches away from latching on to a throughball.
Oliver Burke was introduced as the visitors continued to push forward and he almost teed up Rondon for a last-gasp leveller but for a crucial touch from Butland.
With Albion fully committed in their opponent's half of the pitch, Choupo-Moting and Sobhi found themselves clean through in stoppage time, with the former squaring for the Egyptian to slot into an empty net.
ALBION: Foster, Nyom, Hegazi, Evans (c), Gibbs (Burke 81), Livermore, Barry, Brunt, McClean (Chadli 46, Rodriguez 61), Robson-Kanu, Rondon.
Subs: Myhill, Dawson, McAuley, Yacob.