First-half goals from Jamie Vardy, Jonny Evans and Kelechi Iheanacho were enough to sink West Brom as Leicester kept a firm grip on the game after the break.
It was Vardy’s first goal in 12 appearances for Leicester in all competitions, ending his longest scoreless run for the club since 2016.
Defender Evans doubled the home side’s lead against his former club in the 26th minute when he headed into the corner of Youri Tielemans.
Iheanacho continued his fine form, going 3-0 when he picked up Vardy’s pass and shot past Sam Johnstone.
Leicester maintained their grip on the game in the second half, but lacked their earlier sharpness in the attacking areas.
Leicester, third, whose implosion at the end of last season cost them a Champions League berth, now has a valuable four-point lead over Chelsea and West Ham, with just six games to go.
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It could have been even worse for the Baggies.