Following Friday's result, in-form Albion are now 12 points clear of third-placed Nottingham Forest who only have another 18 left to play for, and could even be promoted on Easter Monday should results go their way over the next three days.
Having seen Jonas Olsson's header clip a post, James Morrison fired the home side into the lead with a sweetly struck half volley - making him the 19th different scorer in the club's league campaign.
Robert Koren doubled the advantage in first-half injury-time as the Foxes again failed to see off a Chris Brunt ball into the box, before grabbing his second late on, ensuring the Baggies claimed an eighth successive home victory that marks their best sequence since 1948/49.
It was an unhappy return to The Hawthorns for former West Brom assistant and caretaker manager Nigel Pearson, whose side enjoyed a lot of the ball but only registered their first shot on target in the 82nd minute.
And a fourth consecutive defeat means the East Midlands outfit are now in real danger of falling out of the play-off places.
Former West Brom winger Lloyd Dyer was posing a big threat in the early exchanges but the hosts went close to breaking the deadlock after 17 minutes.
Brunt whipped an inswinging free-kick into the area and Olsson beat Chris Weale to the ball in the air but saw his header hit the outside of a post and bounce away for a goal kick.
Weale then made a superb save low to his left to flick Ishmael Miller's rasping drive to safety.
Leicester's passing football was proving easy on the eye in the middle of the pitch but it was Albion who were posing the bigger threat in the final third.
And after a significant lull in proceedings it was they who grabbed the opener in style with 38 minutes played.
Brunt's left-wing cross was headed clear by Jack Hobbs as far as Graham Dorrans on the edge of the area and he touched the ball off for Morrison to drill home a sweet strike off the post from 25 yards.
Leicester were soon presented with a mountain to climb as the Baggies grabbed a second goal in similar circumstances.
The visitors failed to deal with yet another Brunt set-piece and Hobbs' headed clearance bounced off Andy King and fell kindly for the unmarked Koren to fire a scuffed effort into the bottom corner.
Steve Howard should have reduced the deficit shortly after the restart but the veteran striker pulled two chances wide with just Scott Carson to beat.
Both sides were afforded half chances during the second half. Having seen Bruno Berner's handball in the area go unnoticed, it was Koren who latched on to Morrison's throughball to round Weale and settle matters.
Leicester substitute James Vaughan was denied a consolation goal by a block on the line in the closing stages as Roberto Di Matteo watched his side move to within touching distance of an immediate return to the Premier League in what was only his 100th match as a manager.