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Gylfi Sigurdsson rejoined Swansea this summer after a spell at Tottenham

Van Gaal's Man Utd reign starts with defeat

United's first opening-day loss at home since 1972

Swansea's first league win at Man Utd

Louis van Gaal's first competitive game as Manchester United manager ended in a historic home defeat at the hands of Swansea City.

A day that began with the Dutch manager receiving a rapturous welcome from the Old Trafford fans as he walked out before kick-off ended with his side being beaten at home on the opening day of the league season for the first time since 1972.

Not even a trademark Van Gaal tactical switch could save him from opening his Premier League account with a 2-1 loss, as his side produced a disjointed performance which underlined the scale of the job ahead of him - and the improvement needed in several areas.

Van Gaal takes responsibility for defeat

Injuries, together with a lack of summer arrivals, saw Van Gaal give debuts to two young academy products - Tyler Blackett on the left of a three-man defence and Jesse Lingard at wing-back.

Midfielder Ander Herrera was the only new signing to line up for a United side that finished seventh last season, and it showed.

Wayne Rooney's overhead kick in his first game since being named United's new captain cancelled out Ki Sung-yueng's opener for the Welsh side, but some uncertain defending allowed new Swansea midfielder Gylfi Sigurdsson to score a 72nd-minute winner.

That saw the Welsh side, who also enjoyed a famous victory at Old Trafford in the FA Cup last season, ruin Van Gaal's big day by clinching their first away win over United in the league in 12 visits dating back to 1931.

Former Netherlands international Ruud Gullit on BBC Match of the Day "Van Gaal has a big job. The Premier League is different. You can see during the game the United players were thinking about where they had to be. When he played 3-5-2 for the Netherlands it was necessity because we had bad defenders. If you were a Swansea player would you have been afraid of that line-up?"

Few people had given Garry Monk's side a chance following a summer in which they had sold defenders Chico Flores and Ben Davies and sent Michu on loan to Napoli.

United, who won all six matches of an impressive pre-season campaign, were certainly the better side early on.

Setting up in Van Gaal's favoured 3-4-1-2 formation, they had wing-backs Ashley Young and, until he was taken off injured, Lingard getting forward well to put Swansea under pressure.

Man United 1-2 Swansea: Garry Monk hails 'great day' for Swans

But the deliveries that came in from the flanks were not good enough to test the visitors and, worryingly for Van Gaal, his defensive trio and the support they were receiving was looking less than convincing.

There were alarming gaps between Chris Smalling in the centre of his back three and Blackett and Phil Jones to his left and right but, while United had the ball, it was not a huge problem.

When Swansea broke, however, it was a different matter and after a couple of scares they punished United after 28 minutes.

No-one tracked Ki and he was left free to meet Nathan Dyer's pass across the edge of the box and slot past David de Gea and into the bottom corner.

The goal brought only shocked silence from the home fans, and no visible reaction from Van Gaal. That only came with the tactical change he made at half-time.

Nani replaced Javi Hernandez and United switched to a 4-2-3-1 shape, with Young and Jones at full-back, and United instantly looked more dynamic and dangerous.

Back with a bang Gylfi Sigurdsson has scored eight goals in 19 Premier League appearances at Swansea. He took 58 games to reach the same number at Tottenham, who he left this summer to rejoin the Swans.

Even so, Swansea will feel they could have done more to stop Rooney's equaliser after 53 minutes, with Jones allowed a crucial flick at the near post that carried the ball to the England striker.

More home goals looked most likely at that stage but the closest United would come to taking the lead was when Rooney fired a curling free-kick against the outside of the post.

Instead, after the home side's forward play reverted to aimless balls forward, it was Swansea who found the net, again, making the most of some uncertain defending.

Young failed to deal with substitute Jefferson Montero's cross at the far post and Wayne Routledge's mis-hit volley fell for Sigurdsson to bury the bouncing ball.

Van Gaal, who stayed in his seat scribbling furiously throughout the match, still had 18 minutes to salvage something from his first game but some desperate late defending saw Swansea hang on.

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Ki Sung-yueng found the net as Wilfried Bony tussled with Phil Jones

Wayne Rooney, preferred to Robin van Persie as Louis van Gaal's captain, scores the first goal of the Dutchman's reign

Manchester United fan Rory McIlroy showed off the spoils of his Open victory at half-time

Ryan Giggs (left) has stayed on as assistant manager after finishing his playing career at the end of last season