ALBION'S perfect home record was blown away during a first-half Cardiff goal blitz which had Premiership quality stamped all over it.
The Baggies had failed to concede en route to winning their opening four Hawthorns fixtures - yet incredibly found themselves 4-0 down inside 29 minutes.
Ex-Liverpool legend Robbie Fowler's second double in three days sandwiched a thunderbolt from former Chelsea hero Jimmy Floyd Hasselbaink.
And Trevor Sinclair, who graced the top flight with the likes of QPR, West Ham and Manchester City, confirmed City's Carling Cup fourth-round berth with a clinical right-foot finish.
Ishmael Miller's third of the season in the 32nd minute ensured a bizarre first-half, during which Albion had enjoyed the lion's share of possession, ended on a minor positive.
The Baggies refused to lie down after the break but, despite pegging Dave Jones' men back for long spells, only had a late Miller penalty to show for their efforts as City recorded their first win at the Black Country venue for almost 51 years.
Mowbray rang seven changes for the first-ever League Cup meeting between the two Championship sides.
Centre-half Shelton Martis made his Albion debut while Jared Hodgkiss, Tininho, Pele, Craig Beattie, James Morrison and Richard Chaplow also earned recalls.
Cardiff named a full strength side which meant the Baggies' new-look defence would have to contend with former top-flight terrors Fowler and Hasselbaink.
And it took Fowler just three minutes to do what no other visiting player had done this term - score.
A flowing City move allowed skipper Stephen McPhail to whip a low cross into the danger-zone and the unmarked Fowler took one touch before blasting past skipper-for-the-night Dean Kiely from 12 yards.
Albion thought they'd produced an immediate response when Miller planted Tininho's centre into the net at the second attempt - only for his goal joy to be nipped in the bud by an offside flag.
Despite their many changes, Albion pushed forward fluently and Miller saw a half-chance flash just over the bar after he had held off City defender Glenn Loovens on the edge of the box.
In the ninth minute, Beattie skipped past Tony Capaldi and McPhail to charge into the box and saw his near-post drive blocked by Bluebirds keeper Michael Oakes.
An off-balance Chaplow fired the rebound wide.
Great inter-play between Chaplow and Morrison then sent Miller clear of the Cardiff defence, but the on-loan striker's effort was well blocked by Oakes at his near post.
But Cardiff struck again in the 22nd minute - with the first of three goals in just seven minutes.
Hasselbaink turned into space 25 yards out and beat Kiely all ends up with a right-foot rocket which nestled inside the far top corner.
Things got worse in the 27th minute when City midfielder Joe Ledley burst into the box and was brought down by Martis.
Fowler made no mistake with the penalty, calmly sending Kiely the wrong way.
In the 29th minute, Cardiff's stats read four shots, four goals.
Tininho, making his competitive home debut, could only direct Capaldi's cross into Sinclair's path and the ex-England winger clinically drilled the ball inside the far post from 15 yards.
A shell-shocked Hawthorns was briefly on its feet when Chris Brunt whipped a 25-yard free-kick just over the angle of post and bar.
And there were muted celebrations in the 32nd minute when Miller made it 4-1.
A terrific Albion move appeared to have come to a luckless end when Morrison rattled the post from 20 yards.
The ball rebounded to the edge of the box, which Miller raced onto before jinking inside Capaldi and drilling low inside the near post.
Albion's goal proved the final action of a truly incredible half.
Mowbray rang two changes at the break, replacing Pele and Chaplow with Jonathan Greening and Filipe Teixeira.
Man-of-the-moment Teixeira soon livened up proceedings, collecting Miller's lay-off and charging at the Bluebirds defence before firing well over.
But Cardiff still looked dangerous when they poured forward and central defensive pairing Martis and Martin Albrechtsen both had to produce key interceptions to deny Ledley and Hasselbaink.
To their credit, Albion gave the second half a right good go and Brunt came within inches of pulling another goal back when he bent a sublime 25-yard free-kick into the side-netting.
Again Cardiff sprung forward on the counter-attack and Kiely had to be alert to race off his line and beat Hasselbaink to the ball in the nick of time to cut out Fowler's attempted through-pass.
The Baggies were soon back on the attack and Brunt wasn't too far away with a downward header from Beattie's hanging cross.
It then took a frantic goalline clearance from Sinclair to deny Beattie a tap-in after Albrechtsen had headed Greening's short corner across the face of goal.
Albion hands were on their heads again in the 70th minute when Brunt's vicious centre deflected off Cardiff duo Loovens and Ledley before spinning agonisingly wide.
Mowbray made his final change a minute later, replacing Beattie with Sherjill MacDonald.
And the Dutch Under-21 striker almost made an instant impact, twisting his way into the box before seeing his goalbound shot blocked by Roger Johnson.
Miller was then unbelievably denied twice in the six-yard box by Capaldi and Loovens' last-ditch blocks after Brunt's corner wreaked havoc in the Bluebirds penalty area.
Albion were awarded an 87th-minute penalty when Sinclair upended Miller just inside the box.
The Moston menace made no mistake, coolly sending Oakes the wrong way.
Albion continued to attack during the dying stages but simply ran out of time.
ALBION (4-1-4-1): Kiely; Hodgkiss, Martis, Albrechtsen, Tininho; Pele (Greening HT); Beattie (MacDonald 71), Morrison, Chaplow (Teixeira HT), Brunt; Miller. Subs not used: Steele (gk), Barnett.
CARDIFF (4-4-2): Oakes; McNaughton (Gunter 78), Johnson, Loovens, Capaldi; Sinclair (Whittingham 87), Rae, McPhail, Ledley; Fowler (Parry 71), Hasselbaink. Subs not used: Turnbull (gk), Green.
GOALS: ALBION - Miller (32 & 87 pen). CARDIFF - Fowler (3 & 27 pen), Hasselbaink (22), Sinclair (29).
BOOKINGS: CARDIFF - Capaldi (foul 33), Loovens (foul 63), Ledley (foul 67).
REFEREE: P Walton (Northamptonshire).
ATTENDANCE: 14,085.
ALBION STARMAN: Ishmael Miller.
PIC: JUMP TO IT...Hodgkiss in action against City
