The pressure was on Nigel Adkins’ side following West Ham’s 2-1 victory over Nottingham Forest at Upton Park on Saturday.
They made a nightmare start as they found themselves 2-0 down inside 26 minutes and never recovered as Nigel Pearson celebrated a winning return to Southampton — having been manager for three months in 2008 — with Leicester triumphant for only the second time in eight league games.
Leicester took the lead in the 15th minute when former Portsmouth striker David Nugent cut in from the left and curled a fine 20-yard effort past the despairing dive of goalkeeper Kelvin Davis.
It was 2-0 in the 26th minute. Republic of Ireland international Sean St Ledger, back in the Leicester side, picked up the ball on the left and delivered an inch-perfect cross for fellow defender Matt Mills to head home his first goal for the club — his last coming for Reading in last season’s play-off final defeat to Cardiff.
Southampton were struggling to create anything threatening offensively, the closest they came was when Dean Hammond headed a Dan Harding free-kick across the face of goal.
Jack Cork then fired over when well-placed four minutes before the break after good work from Morgan Schneiderlin.
Shortly after the restart Nugent curled a shot wide as Leicester looked for a third, but Saints came close to pulling one back in the 53rd minute, Schmeichel doing well to keep out Hammond’s header.