The Wembley-bound Eagles came close to a perfect start when Jean-Philippe Mateta rattled a strike from the edge of the penalty area against the crossbar, but that was still their only effort by the time Paul Onuachu planted a header straight at Dean Henderson in the 18th minute.
Undeterred by giving the goalkeeper catching practice, Onuachu tried again with his head two minutes on following Mateus Fernandes’ cross, and this time the goalkeeper got a touch but could not keep it out and the Saints had the lead.
Oliver Glasner’s side were struggling to create opportunities against their well-rested opponents, and it wasn’t until the 36th-minute when they forced Aaron Ramsdale into a save – the England international got down quickly to deny Mateta.
As Mateta continued to be the visitor’s dangerman, Onuachu continued to play that role for the hosts, but could not find the target late in the half after Palace surrendered possession deep inside their own half.
Attempting to win five Premier League away games in succession for the first time, Palace made a brighter start to the second half, though an Eberechi Eze chance flying just wide was their best chance.
Eze was given another sight of goal after 65 minutes, but again he could not find the target with his free-kick.
Southampton failed to have a shot on goal in the second half, though they were rarely threatened by a Palace team who looked a shadow of the side that had lost just twice in 2025.
That was until deep into added time, when substitute Matheus França leapt high to meet Jefferson Lerma’s cross to equalise and break the home side’s hearts.
That goal extends Palace’s unbeaten league run to four matches, and while Southampton are still yet to reach Derby County’s record-low 11 Premier League points, they at least avoid becoming the third English club to lose 10 consecutive top flight home games.
Flashscore Man of the Match: Paul Onuachu (Southampton)