SOMEN Tchoyi punished another goalkeeping gaffe to send Albion marching into the Carling Cup quarter-finals for the first time in seven years.
In an almost carbon copy of the incident that led to the former Red Bull Salzburg ace bagging an equaliser at Old Trafford ten days ago, Tchoyi tapped the Baggies into a 2-1 lead on 63 after Foxes keeper Conrad Logan inexplicably spilled Gianni Zuiverloon's centre.
Two-goal Simon Cox had earlier seen his deft 21st-minute opener cancelled out by luckless sub Nicky Shorey's 53rd-minute own goal.
But Roberto Di Matteo's men's progress into the last eight was rarely in doubt and skipper-for-the-night Steven Reid's first goal of the season ten minutes from time was richly deserved.
Cox then made it 4-1 in the final minute with a 30-yard cracker.
Albion have never lost to Leicester in the League Cup, nor at the Walkers Stadium, and this victory means they have negotiated a second successive calendar month unbeaten in all competitions.
Having rung as many as 21 changes in the previous two rounds, Di Matteo named a completely new team for this all-Midlands match up.
Sven-Goran Eriksson followed suit, making eight alterations, and the number of switches no doubt contributed to a rather low key opening to this, the fifth meeting between the two clubs in the competition.
During the first ten minutes, the only incident of any note saw the flawless Pablo Ibanez get in a vital last-ditch challenge to deny Yuki Abe a sight of goal after a slick Foxes passage of play.
Then, in the 12th minute, Ibanez had to make a similar intervention to halt ex-Baggie Lloyd Dyer after he had skipped past Marek Cech, who was returning from a two-month foot injury absence.
Albion, backed by almost 4,000 fans, were struggling to get any forward momentum going and Paul Gallagher caused concern when he whipped a 30-yard effort inches wide of Boaz Myhill's far post.
After the Baggies lost possession just inside the City half, Eriksson's men piled forward and Myhill had to show a safe pair of hands to hold onto Dyer's 20-yard grass-cutter.
But Di Matteo's men kept their shape, remained patient and broke the deadlock on 21 - albeit against the run of play.
Giles Barnes skipped past Bruno Berner down the right and his deep cross was hooked back by Tchoyi to Roman Bednar. The lone striker's turn and shot was deflected into the path of Cox, who beat Logan with a delightful dink from ten yards.
City responded with a mini spell of pressure and Myhill had to be alert to deny skipper Steve Howard.
But Barnes had really come to life and he earned his team some respite with a stunning right-wing run, beating both Berner and Miguel Vitor before seeing his vicious cross narrowly evade Bednar's outstretched boot on the edge of the six-yard box.
The ex-Derby man was at it again on 28, and after neat link-up play with Zuiverloon and Bednar, the winger fired straight at Logan from 20 yards.
Albion now looked dangerous every time they attacked but they had a let off at the other end on 32, when Gallagher curled a 30-yard free-kick inches wide of the left-hand post.
Back came Albion and Tchoyi flashed a great effort across the face of goal after exchanging a neat one-two with Bednar.
The Baggies were asking all the questions as the half drew to a close.
And Logan had to produce a fine one-handed save to keep out Bednar's header after the Czech international had inexplicably been allowed to ghost into the box unmarked to meet Graham Dorrans' pinpoint diagonal pass.
Di Matteo rang a change at half-time, with Shorey replacing Cech.
Albion remained on the front foot after the restart and Tchoyi played Dorrans in with an exquisite reverse pass, only for the Scotland international to chip the ball past Logan but harmlessly wide of the far post.
Moments later, the Foxes, who are fourth-bottom in the Championship, hit the Baggies on the break and Shorey denied Dyer a tap-in from Gallagher's cross with a vital far-post clearance.
But Shorey's next touch inside the Baggies box, in the 53rd minute, squared up the tie
After Dorrans lost possession to Franck Moussa as Albion attempted to break from a Leicester corner, Gallagher whipped the ball into the penalty area and Shorey inadvertently diverted it past Myhill with his outstretched boot.
Albion regrouped but Dorrans fired a tame shot straight at Logan after charging onto Cox's throughball.
The Baggies were beginning to get on top again and Bednar failed to hit the target with a great headed chance from Barnes' electric run and cross.
The tie had really opened up and Myhill was relieved to see Abe fire wide from 20 yards.
But Albion were back in front on 63 as Tchoyi profited from a goalkeeping howler for the second time in three games.
After Edwin van der Sar had gifted him a tap-in at Old Trafford, it was déjà-vu time for the Cameroon international as Logan, under no pressure whatsoever, dropped Zuiverloon's diagonal ball, allowing Tchoyi to fire into an empty net from ten yards.
Leicester looked shell-shocked but they gradually regrouped and Ibanez did well to get in the way of Abe's 20-yard exocet after Albion had only half-cleared a corner.
Moments later, Gallagher fired harmlessly over from the edge of the box.
Albion hunted a killer third goal as the game entered the final ten minutes and Logan went some way to making amends for his earlier mistake by producing his best save of the night to tip over Shorey's 20-yard free-kick.
But it was a momentary reprieve.
From Barnes' ensuing corner, Reid rose highest at the far post to make it 3-1 with a downward header.
Logan came to Leicester's rescue two minutes later when he denied the impressive Barnes with his legs.
But a fourth goal was coming and Cox saved Albion's best until last.
The former Swindon marksman pounced on a loose ball before beating Logan all ends up with a 30-yard pile-driver which nestled in the top right-hand corner.
Only another smart Logan save in stoppage time denied late sub Ishmael Miller a goal on his long-awaited comeback from injury.
LEICESTER (4-2-3-1): Logan; Neilson (Lamey 71), Morrison, Vitor, Berner; Abe, Moussa; Dyer (Wellens 54), King (Fryatt 67), Gallagher; Howard (c). Subs not used: Weale (gk), Teixeira, Kennedy, Hobbs.
ALBION (4-2-3-1): Myhill; Zuiverloon, Meite (Mantom 80), Ibanez, Cech (Shorey HT); Reid, Dorrans; Barnes, Cox, Tchoyi; Bednar (Miller 85). Subs not used: Carson (gk), Mattock, Jara, Tamas.
GOALS: LEICESTER - Shorey (own goal, 53). ALBION - Cox (21, 90), Tchoyi (63), Reid (80).
BOOKINGS: ALBION - Meite (foul 32)
REFEREE: A Taylor (Manchester)
ATTENDANCE: 16,957 (3,938 Albion fans)
ALBION STARMAN: Giles Barnes.
PIC: COX IN THE BOX...Simon celebrates after breaking the deadlock