Gylfi Sigurdsson's smart finish gave Swansea City a surprise 2-1 win at Manchester United as the Louis van Gaal era started in defeat.
The Iceland midfielder scored the winner 18 minutes from time as Van Gaal, who has been tasked with improving the fortunes at Old Trafford after David Moyes last term, endured a day he will want to forget in his opening Barclays Premier League fixture.
United struggled in the Dutchman's 3-4-1-2 system and they found themselves behind when Ki Sung-yueng scored from 20 yards just before the half-hour.
Van Gaal swapped to 4-4-1-1 in the second half and it appeared to be the tonic for United's response, led by new captain Wayne Rooney, who levelled with a overhead kick eight minutes after the break.
Rooney saw his outstanding free-kick crash against a post with 24 minutes left and Old Trafford was stunned when Sigurdsson, Swansea's main signing of the close season, finished well after Wayne Routledge's cut-back.
The victory was Swansea's second at Old Trafford in 2014, and second ever, after the Welsh club also won a third-round FA Cup tie by the same scoreline in January.
Van Gaal gave 20-year-old defender Tyler Blackett a Barclays Premier League debut, while Spanish midfielder Ander Herrera and Jesse Lingard also made their top-flight bows.
Lingard started in the unfamiliar position of right wing-back and was nearly caught out just six minutes in, when Routledge drifted across him untracked, but the Swansea man's first touch meant that Jonjo Shelvey's clever ball in behind was squandered.
Sigurdsson, who is back at Swansea for a second spell, this time permanently, after signing from Tottenham Hotspur, saw his 25-yard shot in the 12th minute fall awkwardly for United goalkeeper David de Gea, but the Spaniard did well to smother it.
Lingard was injured in a challenge with Ashley Williams and replaced by Adnan Januzaj, before the hosts eventually got going, with Lukasz Fabianski, the only debutant for the visitors from the start, needing to be alert to keep out Phil Jones' deflected cross and then Juan Mata's inswinging effort.
Swansea converted one of their chances, though, as Ki delighted the travelling fans in the 28th minute. The South Korea midfielder was played in by Sigurdsson, who had initially linked with Nathan Dyer, and he hit a sweet left-footed effort that curled into the right corner from 20 yards.
Van Gaal's men failed to mount a significant response before the break and as a result, the manager replaced Javier Hernandez with Nani and a changed system.
Rooney produced the equaliser eight minutes into the second half, showing great anticipation to thrash Jones' near-post flick-on home from four yards in sensational style.
The England forward continued to threaten, with Williams required to deny him with a last-gasp tackle, before he was thwarted by the woodwork as his 25-yard free-kick left Fabianski rooted to the spot, but crashed back off a post.
Swansea made the hosts pay for their profligacy as a quick free-kick, taken by Wilfried Bony, set them free. A cross from substitute Jefferson Montero made its way through to Routledge at the far post, and although he slipped, his ball fell for Sigurdsson, who hammered an effort through a sea of bodies that was too hot to handle for De Gea.
United, so often saved by late goals, had claims for a penalty denied after Januzaj's cross struck the arm of Angel Rangel in injury time, as Swansea claimed an excellent win.
Manchester United Louis van Gaal: “We don't reach our level, what we have showed in the past matches, and that is disappointing because this is the most important match.
"We are disappointing [in] defence and we are disappointing ourselves. And that's why we lost today. Of course we need defenders, but that I have already said in former press conferences. You cannot say because of one game that we lost, and all the others we won, that it is the defence [that cost them]. It is the team and how we played today. We never played as a team, I think. That is our error."
"We scored a fantastic goal and then we have chances to make it 2-1. But chances is not enough. At the end the result is counting. We have to evaluate why. They [players] have done their utmost best…the second half, they have run all the miles together. But we have to always keep the heads up."
Swansea City manager Garry Monk: "I'm happy but not because it was against Manchester United because all I care about is the three points. That's what I made the players worry about all week. I told them not to care it was Manchester United, the first game of the season, with all the nerves.
"I reminded them it was just another grass pitch and 11 players against 11. It's not that Old Trafford has lost a fear factor - this is Manchester United with the history it is steeped in, the resources they have, the players out on the pitch even considering the injuries they had.
"But I didn't care, all I cared about was us. It doesn't matter where you go, you have to make sure the focus is on what you do, no matter who you play because if you're not right, you'll lose the game. We were right in many areas and got the right result.
“I can pretty much guarantee no-one outside of Swansea gave us a hope. So I told the players to go and show exactly what we're about."
|08 Nov 2014||v Crystal Palace (H)|
|26 Oct 2014||v Chelsea (H)|
|14 Dec 2014||v Liverpool (H)|
|29 Nov 2014||v Hull (H)|
|20 Oct 2014||v West Brom (A)|
|22 Nov 2014||v Arsenal (A)|