The Swans' Barclays Premier League season began on a losing note as champions Manchester United put them to the sword at the Liberty Stadium.
Robin van Persie was the chief architect - the Dutch striker controlling a Ryan Giggs pass before turning and shooting past a helpless Michel Vorm in the 34th minute.
Danny Welbeck doubled the lead just two minutes later as the Swans - who saw Michu's 18th minute correctly ruled offside - were left to fight their way back into the game.
And despite seeing Michu and Angel Rangel going close after the break, it was van Persie who showed the killer instant as he found the top corner with a superb strike in the 73rd minute.
Club record signing Wilfried Bony did pull one back in the 83rd minute, the half-time substitute side-footing home into the corner.
But Danny Welbeck's sublime chip in added on time put the icing on the cake for David Moyes' side.
It proved a disappointing start for Michael Laudrup's side, who must now pick themselves up for their Europa League Play-Off first leg with Romanian side Petrolul Ploiesti at the Liberty.
On the selection front, club record signing Wilfried Bony is among the substitutes after a hefty travel schedule in midweek for the Ivory Coast. That means Michu starts up front while summer recruits Jonjo Shelvey - who lends support to the Spaniard after overcoming illness - and Jose Canas make up the midfield trio along with Leon Britton.
Pablo Hernandez is also on the bench as he makes his comeback from a groin problem so Wayne Routledge and Nathan Dyer start out wide while Ben Davies is given the nod at left-back ahead of Wales team-mates Neil Taylor.
SWANS: Michel Vorm, Angel Rangel, Chico Flores, Ashley Williams (capt), Ben Davies, Leon Britton (Wilfried Bony, ht), Jose Canas (Ki Sung-Yueng, 77), Jonjo Shelvey, Nathan Dyer, Wayne Routledge (Pablo Hernandez, ht), Michu.
SUBS: Gerhard Tremmel, Jordi Amat, Neil Taylor, Alejandro Pozuelo.
MANCHESTER UNITED: David de Gea, Patrice Evra, Phil Jones, Rio Ferdinand, Ryan Giggs (Wayne Rooney, 62), Nemanja Vidic (capt), Michael Carrick, Danny Welbeck, Robin van Persie (Anderson, 86), Tom Cleverley, Antonio Valencia.
SUBS: Anders Lindegaard, Chris Smalling, Fabio Da Silva, Shinji Kagawa, Wilfried Zaha.
During a wet afternoon at the Liberty, the game got off to a frenetic start.
After pressing the visitors as soon as they got possession, Michu closed down David de Gea quickly and the keeper's clearance thundered off the Spanish striker but bounced out for a goal-kick.
Phil Jones then replied for United as his rasping volley was tipped over for a corner by Michel Vorm.
Prior to that, both teams picked up bookings, with Jose Canas and Antonio Valencia earning yellow cards for different incidents.
Robin van Persie then had his first taste of goal, his header from a Ryan Giggs cross floating straight into the arms of Vorm.
Then United countered, and Giggs found himself in space 35 yards out with the goal in front of him, but Angel Rangel tracked back in time to cut out the Wales international's attempted pass to Danny Welbeck.
Welbeck was the next to test Vorm, but his low effort was parried wide by the keeper, and then, on 18 minutes the Swans had the ball in the net only for it to be ruled out by the linesman's flag.
Wayne Routledge's trickery won him a yard of space inside the United box, and when his shot was pushed out by de Gea, Dyer's attempt at goal eventually fell to Michu, who found the bottom corner.
But the cheers were short-lived as Dyer was correctly flagged for offside.
Then Michu's determination and perseverance almost broke the deadlock for good as he competed for a high ball with Nemanja Vidic, and the Spaniard managed to chest the ball before poking his effort goalward. But de Gea reacted quickly to turn it around the post and for a corner.
The action continued, and Shelvey's chipped pass led to Nathan Dyer racing on but de Gea just gathered as the winger got his foot to the ball.
Then United struck twice in three minutes.
Firstly, on 34 minutes, Giggs floated a high ball into the box and van Persie controlled before shooting on the turn and into the corner.
Then, with the cheers just dying down from the away end, Evra's cross was turned back by Valencia and Welbeck touched home from two yards to make it 2-0 in the 36th minute.
That proved the last real action of the half as the Swans looked to get themselves back into the game after the break.
Half-time: Swans 0 Manchester United 2
Michael Laudrup made two changes at the break, Pablo Hernandez replacing Routledge and Wilfried Bony coming on for his league debut in place of Leon Britton.
That meant Bony led the line with Michu dropping into the attacking midfielder role with the Swans eager to make a quick start.
Michu was the first to test de Gea, his 25-yard left-footed effort initially being parried by the keeper before he collected under pressure from Dyer.
The United keeper then had to react quickly to deny Michu after Bony had nodded down Rangel's cross, with de Gea touching the ball out for a corner.
United responded through van Persie, the Dutchman firing across the face of goal after Valencia headed on a de Gea clearance.
Then, at the other end, Hernandez volleyed wide from Rangel's cross before Canas had to clear Patrice Evra's header off the line.
The Swans kept plugging away, though, and Rangel's volley from a Hernandez cross whistled past the top corner, but United - and van Persie - showed their class to finish the game off in the 73rd minute.
The Dutch striker took play on and cut back onto his left foot before thundering his shot into the top corner past the helpless Vorm.
With the game heading into the final moments, Bony flashed a header wide from ten yards before he pulled one back.
In the 83rd minute, after neat work from Dyer and Hernandez, the latter touched to Bony, who hit his shot first time into the bottom of the net.
It mattered little, however, as Welbeck's delicate chip beat Vorm in added on time ensured United started life under David Moyes in perfect fashion.