Goals from Joel Ward and Wilfried Zaha helped Crystal Palace pile more misery on out-of-form Southampton in a 2-1 FA Cup third-round victory.
Southampton headed into Saturday's contest at St Mary's having won just once in their past nine matches, albeit that coming in a 4-0 win over Premier League leaders Arsenal.
And Ronald Koeman's side were 1-0 down at half-time as Ward, who started his career with Saints' rivals Portsmouth, finished a fluent Palace counter-attack.
That goal came against the run of play with Shane Long and Steven Davis missing good first-half chances for Southampton and Oriol Romeu levelled from close range early in the second half.
But Palace, who beat Saints at the same ground 3-2 in the fourth round last season, were not to be denied as Zaha's 69th-minute volley delighted the visiting fans.
Southampton betrayed any nerves from their recent poor run to dominate the opening stages and Long had the first opportunity when he raced clear to round Wayne Hennessey, but the angle was tight and the Palace goalkeeper scrambled back to make the save.
Palace were uncharacteristically sloppy at the back and Davis glanced a free header wide from Cuco Martina's cross.
But Southampton were caught by a sucker punch in the 29th minute.
Jordie Clasie gave the ball away in his own half and former Saints attacker Jason Puncheon raced clear down the right before cutting the ball back for Ward, who rifled home from eight yards.
Palace had a great chance to go into the break 2-0 up, but Scott Dann glanced Puncheon's whipped corner wide when unmarked in the area.
And that proved costly six minutes after the restart as Saints levelled when Romeu played in Martina and, although his shot was saved by Hennessey, the former continued his run to prod in the equaliser.
Southampton were in the ascendancy again following the equaliser and Hennessey did brilliantly to parry Long's edge-of-the-box effort to safety.
But Palace regained the lead with just over 20 minutes remaining.
Maarten Stekelenburg made a terrific stop to prevent Puncheon's curling effort, but the rebound fell to Zaha and he brilliantly controlled a volley into the unguarded goal.
Southampton pushed for a second equaliser and Hennessey made another fine stop from Juanmi's snap-shot, before Virgil van Dijk headed James Ward-Prowse's corner against the post in the last minute as Palace held on to put their name in the hat for round four.