Danny Higginbotham's injury-time goal threw Southampton a lifeline and denied Crystal Palace a win which would have taken them out of the drop zone.
Higginbotham stabbed in Kevin Phillips' cross in at the far post after Palace sub Nicola Ventola's goal looked like giving the hosts a vital victory.
Fitz Hall fired Palace ahead against his former team, before Peter Crouch levelled from the penalty spot.
But Crouch and Palace defender Gonzalo Sorondo both saw red after a melee.
As expected with so much at stake, it was a fraught, nervous, tense opening.
Southampton twice got behind the Palace defence early on, but first Henri Camara and then Olivier Bernard pulled back inviting crosses only to see them go begging.
Crouch kept a cool head and then lost it
Saints appeared to settle the quicker of the two teams, not that there was much flowing football on display.
Hall was determined to make Southampton regret their decision to sell him earlier in the season, and coped manfully early on with Crouch's aerial threat.
Hall was lucky not to concede a penalty when he appeared to haul Camara back when the Senegal striker got goalside.
But the former Oldham defender made a crucial contribution at the other end when he fired Palace ahead on 34 minutes.
Saints' defence failed to deal with Michael Hughes' free-kick and when the ball dropped to Hall he spun to curl a shot past Antti Niemi.
Palace's lead lasted less than two minutes when Popovic handled as Camara flicked the ball up.
Crouch managed to hold his nerve amid delays for the ball blowing off the penalty spot to bury his kick low to Gabor Kiraly's right.
It was Palace who made the more confident start to the second half, although they lacked conviction to commit players forward to provide Johnson with support.
Hall did serious damage to his former club
Palace were building momentum but Southampton defended more doggedly than they did against Norwich.
With the price so high, there was inevitably going to be a flashpoint and when Sorondo and Crouch tangled it sparked a mass shoving match on the touchline.
It ended with both Crouch and Sorondo being shown a red card which rules them out of their final games.
With one point of little use, both managers gambled and sacrificed defenders for strikers.
It was Iain Dowie's substitution that paid dividends as Ventola chased a hopeful ball over the top and with Southampton vainly appealing for offside, drilled the ball past an exposed Niemi.
But with victory and possible safety in sight, Palace switched off at the back and Higginbotham sneaked up at the far post to stab home his first goal of the season after Phillips was given time to turn and cross.
Crystal Palace: Kiraly, Hall, Popovic (Ventola 64), Sorondo, Granville, Routledge, Leigertwood, Riihilahti (Watson 64), Hughes, Soares, Johnson.
Subs Not Used: Speroni, Freedman, Lakis.
Sent Off: Sorondo (59).
Booked: Johnson, Hall, Ventola.
Goals: Hall 34, Ventola 72.
Southampton: Niemi, Telfer, Lundekvam, Higginbotham, Bernard, Oakley (Delap 76), Redknapp (McCann 79), Quashie, Le Saux (Phillips 63), Camara, Crouch.
Subs Not Used: Smith, Davenport.
Sent Off: Crouch (58).
Goals: Crouch 37 pen, Higginbotham 90.
Referee: H Webb (S Yorkshire).