James Ward-Prowse and Jay Rodriguez netted for the home side in the first half and Dusan Tadic struck a late penalty to edge the reigning champions ever-closer to the Premier League relegation zone.
Claudio Ranieri made three changes to the team that was humbled 3-0 by Chelsea last time out. Shinji Okazaki replaced Ahmed Musa, while Demarai Gray and Danny Simpson returned to the side in place of Marc Albrighton and Ben Chilwell.
Elsewhere, the Saints made one change from the team that was defeated 1-0 by Burnley; Jay Rodriguez starting in place of Shane Long.
Saints soar early on
It was the home side who started the better within the first ten minutes and it was Dusan Tadic who was the inspiration. Putting an excellent cross into the Leicester box, he found Nathan Redmond who wasted a chance with a header that was just too high.
Jay Rodriguez then should have scored with a header of his own but nudged it wide of the far post with Kasper Schmeichel scrambling. It was the Dane who then preserved the Foxes' clean sheet not long after. Tadic again whipped in an excellent low ball to find Redmond in space. The England U21 international fired towards the bottom corner but the Leicester stopper was down well to parry away.
The Saints though didn’t have to wait long to open the scoring. Cedric Soares found considerable space on the right wing and passed the ball inside to James Ward-Prowse. The Englishman then swept the ball into the far corner with his right foot to the delight of the home supporters.
Jay Rodriguez then extended his team’s lead in the closing stages of the first half. Awarded a free kick 35 yards from goal, Ward-Prowse whipped the ball into the Leicester box. Attempting to head the ball away, Robert Huth could only nod the ball down to Rodriguez who smashed the ball into the back of the net from only a couple of yards out.
Big blow for the Saints
Moving into the second period, Leicester needed a reaction and Ranieri hoped that would happen by introducing Marc Albrighton for Nampalys Mendy. Claude Puel also had a change of his own to make as Virgil van Dijk went off injured and was replaced by youngster Jack Stephens only ten minutes into the second half.
Pierre Emile-Hojbjerg should have wrapped the game up for the Saints. A poor back-pass from Christian Fuchs allowed the ex-Bayern Munich man one-on-one with Schmeichel but the midfielder blasted his shot wide.
Wes Morgan should also have done better towards the end to give his side hope. Finding space in the Saints’ penalty area, the Jamaican blazed over with a powerful effort. In fact, the Leicester captain’s afternoon then seemed to get worse as he bundled the ball into the back off the net from a Southampton free kick but it was ruled out via an offside call by Michael Oliver.
The ex-Nottingham Forest man then compounded his side’s afternoon as he brought down Shane Long in the penalty area. Dusan Tadic stepped up hammered the ball into the top corner to seal the victory for the Saints.
As a result, Claude Puel’s men rise to 11th in the Premier League table as the Foxes languish in 15th place.