Wilfried Zaha returned to haunt Manchester United with a deadly double as Crystal Palace landed a dramatic 3-1 win to leave Ole Gunnar Solskjaer reeling.
Just as they did in the early weeks of last season, Palace took all three points from their trip to Old Trafford, as a brittle United team were picked apart.
Andros Townsend hit a seventh-minute opener but the match was still in the balance with around 20 minutes to play when Palace were awarded a penalty, after Jordan Ayew's flick struck the hand of Victor Lindelof.
Goalkeeper David de Gea looked to have made himself a hero when he saved the softly struck penalty from Ayew, only for a re-take to be ordered, and this time former United winger Zaha stepped up to smash the ball high into the net.
United new boy Donny van de Beek pulled one back, but Zaha added a third Palace goal in the 85th minute, holding off weak link Lindelof and drilling beyond De Gea from the edge of the penalty area.
Lindelof's grim outing began when his timid defending allowed Jeffrey Schlupp to send over the low cross from the left that Townsend smashed back across goal from beyond the far post, finding the bottom-left corner to put the visitors ahead.
United peppered the Palace goal but without ever looking genuinely menacing.
Indeed, it was Palace who looked the most potent and Ayew drew a save from De Gea early in the second half before Townsend had a dangerous shot deflected over.
There was relief in the United ranks when Zaha burst through and lashed the ball past De Gea, only to be shown to have run offside.
Yet not even a De Gea penalty save offered the real succour they were seeking. The Spaniard, preferred to Dean Henderson, dived to his right to make a comfortable stop, but he had moved a fraction off his line before the shot and was punished. Ayew handed over responsibility to Zaha, who fired high into the net.
Zaha joined United in January 2013 but barely played for the club before being shipped out on loan to Cardiff and then returning to Palace. Their loss has been the Eagles' gain, with Zaha becoming a Premier League star and frequently linked to bigger clubs.
Van de Beek, on as a substitute, got United back into this game, but Zaha had the final say with his terrific second goal.
What does it mean? United off to a stinker
In United's first competitive game since going out to Sevilla in the Europa League semi-finals, familiar defensive instability was exploited by a daring Palace.
Patrick van Aanholt scored a last-minute winner last season in this fixture, but this time Palace were in control long before the closing stages. On a day when rivals Liverpool and Tottenham made statement signings, United looked stale.
Zaha makes history
Remarkably, Zaha became the first player to have played for United in the Premier League to then score twice in a single game against the Red Devils in the competition. He continues to drive Palace forward, despite continued rumblings over a move elsewhere. They would be a far weaker unit without him.
Lindelof looks a soft touch again
Lindelof made seven clearances, five more than any other United player, but he was nevertheless still at the heart of each Palace goal. Giving away the penalty was unfortunate, with referee Martin Atkinson's decision a tough one to take, but the others could have been prevented, Lindelof not up to the job either time.
United go to Luton Town in the EFL Cup on Wednesday (AEST) and are next back in Premier League action when they face Brighton next Saturday. Palace, with two wins from two in the league so far, tackle fellow fast starters Everton next, on Sunday.