Southampton forced Leicester to a 1-1 draw despite playing more than 80 minutes with ten players, frustrating the Foxes in their bid to finish in the top four.
When Jannick Vestergaard's tackle on Jamie Vardy was considered to have denied the Leicester striker a goal-scoring chance, he was controversially sent off after just 10 minutes.
Vestergaard, the last defender on the line, won the ball with a lunging tackle, but referee Robert Jones ruled that his follow-through on Vardy's ankle stopped the striker from running in on goal.
The game's pattern was set by that decision, with Leicester probing while Southampton defended deep, but the Saints took the lead in the 61st minute.
After Kelechi Iheanacho blocked Stuart Armstrong's attempt with his arm raised over his head, James Ward-Prowse scored from the penalty spot.
Jonny Evans equalized eight minutes later with a header from Iheanacho's cross, but Southampton's defense held firm under near-constant pressure.
In the final ten minutes, goalkeeper Alex McCarthy denied Vardy with his right boot from near range.
With a game in hand on fifth-placed West Ham, Leicester are now eight points clear, but they face a tough finish to the season.
Southampton have moved 10 points clear of the relegation zone and are on the verge of securing their safety.