Saints left it to the last day to display some of their best form of the season, ripping open the Leicester defence almost at will in the first half and then coasting home after the break as Leicester at last offered some resistance.
Nathan Dyer hit the post for Southampton in the sixth minute as the prelude to a dominant display by the home side.
Grzegorz Rasiak shot into the sidenetting before the Saints took the lead in the 23rd minute.
Patrick McCarthy and Richard Stearman got in a tangle to leave Ricardo Fuller the simple task of shooting into the corner of the net.
Southampton went two ahead in the 25th minute with a sweet move started by Andrew Surman in the centre circle and finished by the same player after his sweeping pass had put Fuller clear on the left.
Leicester managed only a 34th minute free-kick from Gareth Williams which briefly troubled Saints keeper Kevin Miller.
Rasiak had a goal disallowed for offside in the 48th minute and Leicester rallied, with Chris Baird clearing off the line from Iain Hume and Matt Fryatt shooting wide from a good position.
But Southampton should have got a third in injury time when David Prutton raced clear from the halfway line only to have his shot blocked by goalkeeper Paul Henderson.
Southampton had Dyer booked for a foul on Andy Welsh and Leicester central defenders McCarthy and Nils-Eric Johansson were also shown yellow cards as Leicester made a late effort to avoid their 18th defeat of the season.
Southampton lost their captain and player of the year Claus Lundekvam with a head injury in the 84th minute, to be replaced by Martin Cranie.