James Ward-Prowse, Jay Rodriguez and Dusan Tadic condemned Leicester to their 11th Premier League defeat of the season as Southampton triumphed 3-0 at St Mary's.
The reigning champions have now lost half their Premier League matches this term, to sit just five points above the relegation zone.
Southampton eased to victory, leaving Claudio Ranieri's Leicester looking short of ideas in attack and worryingly frail at the back.
Saints' cruise-control win was tempered by an ankle injury to captain Virgil van Dijk, leaving Claude Puel's men short of centre-backs after Jose Fonte's Â£8million switch to West Ham in midweek.
England Under-21s cap Jack Stephens filled the breach, and now Saints will hope Van Dijk can recover in time for Wednesday's EFL Cup semi-final second leg at Liverpool.
Leicester's decline continued unchecked on the south coast as last year's defensive linchpins Robert Huth and Wes Morgan were again exposed.
Huth inadvertently laid on Southampton's second goal, his attempt at a headed clearance turning into a knock-down that let the lurking Rodriguez sneak in and finish with relish.
And a potential own goal from Morgan was chalked off owing to a foul from Maya Yoshida. That reprieve hardly spared the visitors' blushes however, with Tadic adding Saints' third with a late penalty.
Southampton dominated from the off, deservedly taking the lead on 25 minutes through a crisp attack.
Van Dijk's raking crossfield pass handed Cedric Soares time to exchange passes with Nathan Redmond and set the Saints off and running.
Redmond then bisected the defence down the inside-right channel, Cedric whipped in a low cross - and Ward-Prowse finished sweetly past Kasper Schmeichel.
Leicester offered precious little attacking merit barring their constant counter-strike threat.
And the Foxes conspired to compound their own misery when Huth headed a lofted free-kick straight into Rodriguez's path for the Saints striker to double the hosts' lead.
Leicester failed to cure their malaise after the break but Saints failed to capitalise, with Pierre-Emile Hojbjerg missing two clear-cut openings in quick succession.
The former Bayern Munich midfielder fired two low shots wide in near carbon-copy situations, the second proving most wasteful.
When Hojbjerg intercepted Christian Fuchs' stray pass and raced through on goal Saints' third appeared odds-on. Schmeichel was left to breathe a sigh of relief though as he watched Hojbjerg's strike fly wide of the upright.
Leicester avoided yet more ignominy when Morgan's own goal was chalked off, for a push by Yoshida. The day was still to worsen for Ranieri and company however, with Tadic firing home emphatically late on from the spot to round off a Southampton win which was all too easy.