Perhaps it really was a dream.
The delight of Selhurst Park, that heady afternoon in the winter sunshine, vanished in the space of 45 minutes.
If you weren't there, you may well be struggling to believe it really happened.
Two goals from Gabbiadini, the second a finish his name-sake would have been proud of, a late own goal, and Sunderland were back to square one, They managed just one shot on target, familiar deficiencies on attack and defence back to the fore.
Oriol Romeu was utterly dominant in midfield, controlling the game. There was never any hint of a great comeback.
The Black Cats had made a reasonable start to the game, making their retreat all the more frustrating.
Though there were some errant passes in the opening 15 minutes, they generally looked more composed, more relaxed and more confident than at many stages this season. They created the best two openings, too, Adnan Januzaj escaping on the edge of the box to see his shot deflected wide. The 21-year-old then burst down the left flank, surging into the box and towards the byline, His cut-back was good but just too strong, Defoe unable to control in the box and the ball rolling out for a goal kick.
That move was built right from the very back, Vito Mannone ambitiously chipping the ball over Manolo Gabbiadini's head to release Jason Denayer. Sunderland looked to have a spring in their step; it didn't last.
A superb first time pass from Oriol Romeu, finding Ryan Bertrand on the left, His cross to the front post was wicked, even if he had far too much space to deliver. Gabbiadini forced it in at the front post, very possibly via his arm and the head of Lamine Kone.
If that was a touch unfortunate, the killer blow just before the half-time whistle was entirely self-inflicted.
The build-up from the Saints was impressive, one touch, crisp passing to release Dusan Tadic. His ball for Manolo Gabbiadini was good, but the ease at which the Italian was allowed to turn away from Kone and John O'Shea was poor, firing under the body of Vito Mannone.
It looked such a long way back, Southampton far more impressive on the counter when their quick front three could be more fluid and instinctive in their movement. David Moyes had seen enough and Steven Pienaar replaced John O'Shea at the break, switching to a flat back four.
It ought to have been three just moments after the whistle. A corner to the back post somehow finding Gabbiadini, but his first time volley was straight at Mannone. By now the visitors were brimming with vigour and purpose, the confidence Sunderland had built last weekend all but drained.
Saints were hardly rampant but they didn't need to be, moving the ball efficiently and keeping the play well away from their own goal. Dusan Tadic stung Mannone's palms from 25 yards as the atmosphere in the ground spilled from frustration towards outright anger. Ironic cheers met the first save for Fraser Forster, a comfortable collect following a weak effort from Ndong. An effort from a similar distance at the other end came closer, Mannone scrambling as James Ward-Prowse's effort whistled just past the post.
By this point Fabio Borini had replaced Seb Larsson, a move that yielded little extra quality in Sunderland's attacking play. Ward-Prowse somehow failed to make it three with fifteen minutes to play when headed wide from inside the six-yard box. The hosts were now offering precious little in the way of resistance, Shane long the latest to be presented with a free header. Mannone this time was forced into a save, palming over the bar.
Wahbi Khazri's introduction brought a flicker of life, a touch more bravery on the ball, but it was too little too late, the rout completed when Jason Denayer turned Bertrand's cross into his own net.
The fourth was simply embarrassing, Sunderland simply watching on as Shane Long turned home from inside the box.
A meek, maddening defeat.