ALBION completed only their second-ever Barclays Premier League double with an outstanding second-half display to spoil Blues' Carling Cup party.
The Baggies repeated the scoreline from their Hawthorns victory over City in September to leapfrog their derby rivals into 16th place and move four points clear of the drop-zone - at least for a few hours.
Following a goalless first half, the game exploded into life after the break as Youssouf Mulumbu and James Morrison fired their fourth goals of the campaign in the 47th and 58th minutes respectively.
Jean Beausejour's 48th-minute leveller was sandwiched in-between - but the visitors made sure of three fully-deserved points thanks to Paul Scharner's 72nd-minute header, after Chris Brunt had earlier hit the post.
Albion's first league win on the road since November delighted over 3,100 Baggies fans, who were in full voice throughout at St Andrew's.
Morrison was restored to Roy Hodgson's starting XI as he replaced the injured Graham Dorrans (ankle) in central midfield.
Blues made five changes to their Carling Cup final line-up. Among them were ex-Baggies captain Curtis Davies, who made his City debut at the heart of defence.
Albion fashioned the first chance in the fifth minute when Jerome Thomas stood up a cross for Brunt who could not get enough power on his header to beat Ben Foster.
A minute later, Thomas cut out Roger Johnson's pass to Stephen Carr and skipped past Davies before seeing his shot blocked by a relieved Johnson.
There was plenty of huff and puff but little in the way of creativity, although Abdoulaye Meite did well in the 21st minute to bravely head away David Bentley's dangerous free-kick from in front of goal.
Scharner gifted the ball to Cameron Jerome on 28 and the City striker fired a low 20-yard shot just past the right-hand post.
Jerome won a 50/50 with Brunt in midfield two minutes later and drove towards the box before seeing his shot deflected safely into the arms of Scott Carson.
The Baggies had a golden opportunity to get their noses in front in the 35th minute when Brunt's pass set Thomas free down the left and he comfortably beat Davies to reach the edge of the area.
The former Charlton winger should have found Morrison, who was completely unmarked in the box, but he delayed his pass too long and it was blocked.
The loose ball fell to Brunt, who blazed over from 25 yards.
At the other end, Jerome swooped to head Beausejour's cross a fraction wide of the right-hand post from 12 yards.
Scharner then made a vital interception to deny Jerome as he was about to pull the trigger just inside the box after the ball had dropped kindly for him.
Hodgson made a change at the break as nine-goal top scorer Peter Odemwingie came on for the hard-working Marc-Antoine Fortuné.
And the Nigerian was heavily involved as the game exploded into life within 90 seconds of the restart.
Keith Fahey was unable to control Foster's poor clearance and Mulumbu nipped in and found Odemwingie.
He jostled his way past Beausejour before threading the ball through to Mulumbu who coolly finished over the diving Foster to open the scoring.
But Albion's lead only lasted just over a minute as Lee Bowyer ghosted into space down the right and crossed low into the six-yard box for Beausejour to prod home the equaliser.
The goal briefly sparked Blues into life and Carson did well to back-pedal and punch away Bentley's in-swinging cross that looked to be dipping inside the far top corner.
But Albion were soon back in the ascendancy thanks to some Morrison magic.
The excellent Reid piled forward on 58 and found the Scotland international who coolly dinked the ball past Davies before drilling an unstoppable 18-yard half-volley past a helpless Foster.
A minute later, Carson could only beat out Bentley's fierce 25-yard drive and the rebound fell to Obafemi Martins, who could not get his shot away under pressure from the rock-solid Olsson and Albion were able to clear.
Both sides made a change on 67 as Gonzalo Jara came on for Thomas and former Albion ace Kevin Phillips replaced Beausejour for Blues.
While Brunt was switching to the left wing, with Jara starting on the opposite flank, 'Super Kev' was given a rapturous welcome by the away end as he faced his former club for the first time since leaving in the summer of 2008.
The Baggies came within a whisker of grabbing a third a minute later when Brunt's right-foot strike from 25 yards struck the base of the right-hand post.
The rebound fell kindly to Odemwingie, who hurried his shot when he could have controlled, and he inexplicably drilled wide of the open goal.
But the visitors did add a deserved third in the 72nd minute.
Morrison collected Brunt's short corner on the left and crossed to the back post, where Scharner's header had enough power to beat Foster.
Hodgson made his final change in the 78th minute as Gabriel Tamas came on for Morrison and slotted in at right-back. Reid was moved into central midfield.
Two minutes later, Blues' David Murphy came on for Ridgewell.
In the final ten minutes of the game, the Baggies came close to increasing their lead when Scharner almost lobbed Foster and Odemwingie headed Brunt's left-wing cross horribly wide when he should at least have hit the target.
But the Baggies weren't to be denied their first win at St Andrew's in ten years.
BLUES (4-4-2): Foster; Carr, Johnson, Davies, Ridgewell (Murphy 80); Beausejour (Phillips 67), Fahey, Bowyer, Bentley; Jerome, Martins. Subs not used: Doyle (gk), Larsson, Zigic, Parnaby, Mutch.
ALBION (4-2-3-1): Carson; Reid, Meite, Olsson, Shorey; Scharner, Mulumbu; Brunt, Morrison (Tamas 78), Thomas (Jara 67); Fortuné (Odemwingie HT). Subs not used: Myhill (gk), Cox, Tchoyi, Vela.
GOALS: BLUES - Beausejour (48). ALBION - Mulumbu (47), Morrison (58), Scharner (72).
BOOKINGS: BLUES - Bowyer (foul 51), Ridgewell (unsporting behaviour 52), Fahey (foul 88). ALBION - Scharner (unsporting behaviour 52).
REFEREE: M Jones (Chester).
ATTENDANCE: 27,013 (Albion fans 3,153).
PIC: YOU-SSOUF BEAUTY...Mulumbu celebrates his goal with Odemwingie
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