Salomón Rondón gave the hosts the lead in the eighth minute with a close range finish to give the Baggies some hope. Jamie Vardy though equalised mid-way through the first-half with an excellent volley before second-half strikes from Riyad Mahrez, Kelechi Iheanacho and Vicente Iborra flipped the game on its head and leave Alan Pardew's team teetering towards relegation.
Leicester boss Claude Puel made five changes to the team that drew 1-1 with AFC Bournemouth last time out. The injured Daniel Amartey was replaced by Danny Simpson. Meanwhile, the likes of Shinji Okazaki, Vicente Iborra, Ben Chilwell and Demarai Gray were drafted into the team.
Meanwhile, the under-pressure Alan Pardew made two changes to his Baggies team. Jay Rodríguez dropped out of the side in place of Oliver Burke. Elsewhere, Allan Nyom was called-up in place of the injured Jonny Evans.
Baggies bounce from the off
An excellent predatory finish from Rondón opened the scoring for the hosts barely ten minutes into the game. Burke did well to skip past Chilwell on the left-flank and put in a low cross to the Venezuelan. Getting to the ball just ahead of Wes Morgan, the former Zenit striker, who was making his 100th Premier League appearance, stretched to poke into the net.
Leicester attempted to react to going behind and Vardy was inches away from heading Riyad Mahrez's cross past Ben Foster.
It took an excellent save from Kasper Schmeichel to keep the deficit to one as Grzegorz Krychowiak took aim from distance. The Dane somehow managed to tip the midfielder's spectacular effort onto the crossbar.
Mahrez magical, Vardy clinical
An excellent strike from Vardy was enough to drag Puel's men level. Mahrez found acres of space in midfield and found the speedy forward with an excellent lofted ball. With a sweet, left-footed volley, he sent the ball beyond Foster and into the far corner to score his fourth goal at the Hawthorns in as many games.
As a matter of fact, the 31-year-old could have had another as he diverted Chilwell's low cross low into the net. The linesman correctly intervened however and ruled the goal out for offside.
The hosts continued to probe though and Rondón could well have had another as he raced away from the Leicester defence. An excellent block from Wes Morgan kept the scores level however.
Fiesty opening to second half
The second period really saw the game open up with Leicester in the ascendency. Demarai Gray twisted, turned and looked to cross. The ball took a wicked deflection towards goal with Foster having to intervene with a vital touch.
Puel introduced Kelechi Iheanacho for Okazaki and the ex-Manchester City forward had an instant impact. Using a delicate chip, he found Mahrez who touch a took and lifted the ball over Foster to complete the turnaround.
Iheanacho then continued his excellent contribution as he notched his first Premier League goal for the Foxes. Chilwell found space on the left side and teased in an excellent cross that was duly headed into the net by the Nigerian.
Leicester show no mercy
With the final kick of the game, Leicester made the score-line even worse for the Baggies. Spanish midfielder Iborra manufactured space only yards from goal from a corner and thundered a header into the back of the net.
As a result of their loss, West Brom remain rooted to the bottom of the Premier League table. Leicester meanwhile are in eighth and finally have their first league win since mid-January.