A hat-trick from Japanese forward Shinji Kagawa condemned Norwich City to defeat at the hands of Premier League leaders Manchester United at Old Trafford.

Wayne Rooney added a fourth goal in the final minute to wrap up what was ultimately a comprehensive victory.

United opened up a 15-point gap at the top of the table as the Canaries suffered their first defeat in five league games.

Kagawa scored the first in stoppage time at the end of the first half, after Robin van Persie had flicked on a cross by Antonio Valencia.

The second goal came on 76 minutes when Kagawa sidefooted home from a Rooney pass, and the man from Japan completed his treble from another Rooney assist on 87 minutes.

Rooney floated in a superb fourth to complete a fairly miserable afternoon for Chris Hughton's men, who also picked up four yellow cards.

City had a bright spell early in the second half and at 1-0, Russell Martin should have had the ball in the net when he hooked a shot over, but skipper Grant Holt had already been penalised for a foul.

City's starting line-up showed one change from the 2-1 victory over Everton with Anthony Pilkington recalled at the expense of Luciano Becchio, who dropped to the bench.

Jonny Howson continued in midfield in the absence of Alex Tettey, sidelined by a knee injury.

United showed five changes to the team that started the 2-0 victory at Queens Park Rangers with recalls for Jonny Evans, Antonio Valencia, Anderson, Rooney and Kagawa.

There was no 1,000th senior professional appearance for veteran Ryan Giggs, who was not included in the 18, but striker Van Persie was included after recovering from the hip injury he suffered at Loftus Road, manager Sir Alex Ferguson having declared him fit on Friday.

City made a promising break in the third minute but Johnson spoiled the move with an overhit cross from the left.

Seconds later, Snodgrass was in pain after Kagawa trod on his knee as completed a sliding challenge, but he was back on his feet moments later to tackle Nani.

Bunn raced out to stop Rooney getting on the end of Van Persie's pass as United threatened.

A free-kick by Van Persie was nodded down by Vidic and bounced ominously across the penalty area before City were able to clear.

With 15 minutes gone, Bunn needed attention when he was caught by Van Persie's boot. The Dutchman played a one-two with Rooney and went in hard for the return, leaving the keeper nursing his thigh.

City threatened again when Holt jumped to meet Hoolahan's cross from the left but his header across the six-yard box was claimed by De Gea.

United were putting on most of the pressure, though, and Carrick squeezed in a low shot that Bunn saved to his left.

Vidic headed over the top from a Van Persie corner, and though it appeared Bassong may have got the final touch, a goal-kick was given.

Turner blocked a shot by Rooney after Evra had given Russell Martin the slip, then Rooney forced a corner with a shot that ballooned out via a deflection.

Martin was next to block a shot by Rooney after an inricate passing move as United tried to find a way through.

With 10 minutes to the break, Van Persie was way off target with a shot more akin to a rugby conversion.

Van Persie's header struck Turner in the closing minute of the half, and in first half stoppage time United went ahead through Kagawa, Valencia crossed from the right, Van Persie flicked it past Bassong and Kagawa slotted his shot past Bunn, though he did not catch it cleanly.

There was still time for Snodgrass to be booked for a foul on Evra that had Ferguson protesting to the fourth official.

• Half-time: Manchester United 1, Norwich City 0

Five minutes into the half, City fashioned a move of promise and Vidic had to clear at the near post as Snodgrass challenged for Martin's cross.

Martin had the chance to cross again moments later but his centrre sailed over the head of Holt.

Bunn came out to deny Rooney as Kagawa put him through, poking the ball away amid optimistic appeals for a penalty by the home crowd.

A foul by Vidic on Holt gave City a free-kick 10 yards into the United half, Snodgrass floating it towards Bassong but the defender's header looping into De Gea's hands.

Bassong got his head to a Pilkington corner and as Norwich began to look livelier, Howson's long-range shot deflected wide off Carrick.

It was a bright spell and Martin appeared to miss a golden chance to equalise on 62 minutes when Holt nodded down Pilkington's cross to the far post, but the full-back hooked the ball over the bar with the goal at his mercy. However, referee Swarbrick had penalised Holt for a foul on Evra.

Rooney fired a poor effort wide before United made their first change, Welbeck replacing Van Persie after 66 minutes.

Garrido was booked for a body check on Valencia, who continued to be United's most dangerous looking player.

With 72 minutes gone, Hoolahan made way for Kamara, looking to add to his goal from the previous week, and after Johnson had been booked for a foul on Rooney, there was a double change, Elliott Bennett replacing Snodgrass for Norwich and Anderson making way for Cleverley for United.

But it looked like game over on 76 minutes when Kagawa struck his second of the match.

Carrick's long ball forward was brought under control by Rooney and he stepped inside Bassong to roll the ball perfectly into Kagawa's path for a simple finish.

Bunn made a good save from Welbeck as United threatened a third, after Rooney's run had been blocked off by Turner.

Welbeck was rolling on the ground after a challenge from Turner that led to a belated yellow card from referee Swarbrick, the fourth of the afternoon.

With three minutes left, Kagawa completed his hat-trick with a delicate finish, flicking his shot over Bunn after another Rooney pass.

City were ragged by now and in the final minute, Rooney floated a magnificent fourth goal just out of reach of Bunn.

Becchio replaced Holt before the game restarted in a fairly pointless substitution.

• Manchester United: De Gea; Smalling, Evans, Vidic, Evra; Valencia, Carrick, Anderson (Cleverley, 74), Kagawa; Rooney, Van Persie (Welbeck, 66). Subs (not used): Lindegaard, Rafael da Silva, Nani, Young, Hernandez.

• Norwich City: Bunn; Russell Martin, Turner, Bassong, Garrido; Howson, Johnson; Snodgrass (Elliott Bennett, 74), Hoolahan (Kamara, 72), Pilkington; Holt (Becchio, 90). Subs (not used): Camp, Whittaker, Ryan Bennett, Fox.

• Referee: Neil Swarbrick (Lancashire)

• Attendance: 75,586

• Goals: United: Kagawa (45, 76, 87), Rooney (90)

• Bookings: City: Snodgrass (45), Garrido (69), Johnson (73), Turner (82)