TEN-MAN Albion surrendered an early lead as Steve Howard's second-half hat-trick sentenced the hosts to only their third home league defeat of the season.
Everything looked rosy in the Baggies garden when Robert Koren's deflected shot - his ninth of the campaign - put Tony Mowbray's men ahead in the 22nd minute.
But Albion's world was turned upside down in the space of three first-half minutes when on-loan Luke Moore was red-carded for serious foul play before Gareth McAuley headed City level.
Leicester took full advantage of their extra man in the second half, with Howard converting a controversial penalty in the 59th minute before wrapping up the points with a late double.
Albion started the day some 18 places and 21 points better off than Leicester, who slipped to third bottom after Tuesday's defeat at relegation rivals Southampton.
Mowbray rang four changes, with full debutant Do-Heon Kim, Shelton Martis, Moore and Roman Bednar coming in for the injured Chris Brunt, benched duo Kevin Phillips and Ishmael Miller, and the axed Jared Hodgkiss.
Leicester couldn't get out of their own half during the early exchanges - but almost snatched a tenth-minute lead.
Leon Barnett's weak back header was seized by striker Barry Hayles who charged into the box and rounded Dean Kiely.
But Barnett redeemed himself by racing back and blocking Hayles' goalbound effort out for a corner.
Two minutes later, Matt Fryatt volleyed just over from 15 yards after Barnett had headed away a Joe Mattock free-kick.
It was now Albion struggling to impose themselves on the game, but Matt Oakley failed to trouble Kiely with a 20-yarder which sailed over.
The Baggies regrouped and it took a great last-ditch tackle by McAuley to deny Kim a clear chance from Bednar's clever flick-on.
McAuley was the right man in the right place again seconds later to prevent Bednar stabbing home Zoltan Gera's centre.
But a goal had been coming and it duly arrived in the 22nd minute - in slightly fortuitous circumstances.
Koren collected a loose ball 25 yards out and saw his right-foot rocket deflect off a Leicester defender and fly past wrong-footed Foxes keeper Paul Henderson.
Albion regained control - but had a let off in the 32nd minute.
City skipper Oakley pounced on a loose ball 25 yards out and unleashed a ferocious right-footed shot which whistled inches past the far post.
Albion suffered a huge setback in the 35th minute when Moore was shown a straight red card for a late challenge on Richard Stearman.
Two minutes later, Kiely had to pull off a wonderful one-handed save to keep out Fryatt's 12-yard effort from Oakley's pull back.
But it was a momentary reprieve. From Hayles' ensuing short corner, Mattock swung in a terrific left-wing cross and McAuley rose above the Baggies defence to head powerfully past Kiely.
In the 43rd minute, Kiely was well placed to clutch Howard's header underneath his own crossbar from Mattock's free-kick.
But the Baggies finished the half strongly.
Paul Robinson stretched every sinew in his body to connect with Jonathan Greening's right-wing free-kick and it took a fine, finger-tipped Henderson save to keep out the left-back's close-range volley.
From Greening's ensuing flag-kick, Martin Albrehctsen towered above the Leicester defence but headed wastefully over.
Leicester used their one-man advantage to good effect after the break and Kiely was relieved to watch Howard's header from Stearman's right-wing centre loop onto the roof of his net.
Lee Hendrie then failed to trouble the Baggies goal with a 20-yard volley which trickled well wide.
But Albion fell behind in the 59th minute when Greening was harshly adjudged to have fouled Hendrie just inside the box and conceded a penalty.
Howard made no mistake, smashing a perfect spot-kick to Kiely's left.
Albion were working hard but finding it difficult to contain Leicester.
The Foxes threatened again from a half-cleared corner which Patrick Kisnorbo volleyed straight at Kiely from 20 yards.
Mowbray made his first changes in the 62nd minute, replacing Gera and Kim with Pele and Sherjill MacDonald.
Leicester recorded another effort on goal five minutes later when Fryatt shot straight at Kiely from 25 yards.
Mowbray made his final throw of the dice in the 69th minute when he brought on top scorer Phillips for Bednar.
Albion started to gain the upper hand as the game crept into the final 15 minutes and Phillips saw an 18-yard drive loop off Oakley and into Henderson's out-stretched arms.
But the visitors made the points safe 11 minutes from time when Kiely was unable to keep out Howard's 15-yard strike after neat build-up play by Oakley and Hendrie.
Things went from bad to worse when Albion were forced to play out the final eight minutes with NINE men after Barnett limped off.
Howard completed his treble in the 86th minute by polishing off Hayles' throughball.
ALBION (4-4-2): Kiely; Martis, Barnett, Albrechtsen, Robinson; Gera (Pele 62), Koren, Greening, Kim (MacDonald 62); Moore, Bednar (Phillips 69). Subs not used: Danek (gk), Miller.
LEICESTER (3-4-3): Henderson; McAuley, N'Gotty, Kisnorbo; Stearman, Oakley (Wesolowski 83), Hendrie (Etuhu 88), Mattock; Fryatt, Howard (Hume 88), Hayles. Subs not used: Chambers, Campbell.
GOALS: ALBION - Koren (22). LEICESTER - McAuley (38), Howard (pen 59, 79, 86).
BOOKINGS: ALBION - Kim (foul 15), Robinson (foul 41). LEICESTER - Howard (foul 11), Hendrie (dissent 42), Hayles (foul 45+5), Oakley (foul 60).
SENDING OFF: ALBION - Moore (serous foul play 35).
REFEREE: D Deadman (Cheshunt).
ATTENDANCE: 22,038.
ALBION STARMAN: Jonathan Greening.
PIC: SEEING RED...Moore tussles with Hendrie before his sending off
