Manuel Pellegrini: "I am concerned because we are losing too many points away and, of course, that's very difficult if you don't win away to try to fight for the Premier League.
"But I don't think we are playing badly, so we must have a reaction, we must improve to make sure we are going to win.
"The reaction is very similar to the other games that we have lost away. It's incredible the way we lost this match.
"Sunderland played really well also defending. The team is not in a good position, so I understand the way they played.
"But they had just one shot on our goal. We had the possession, we had the chances and we didn't score."
A review of Sunday's action in the Barclays Premier League .
Robin van Persie downed old club Arsenal to blast Manchester United back into the Premier League title race with a 1-0 victory at Old Trafford as David Moyes enjoyed his biggest win as Red Devils manager.
1 Arsenal 25 2 Liverpool 23 3 Southampton 22 4 Chelsea 21 5 Man Utd 20 6 Everton 20 7 Tottenham 20 8 Man City 19 9 Newcastle 17 10 West Brom 14 11 A Villa 14 12 Hull City 14 13 Swansea 12 14 Cardiff 12 15 Norwich 11 16 West Ham 10 17 Stoke City 10 18 Fulham 10 19 Sunderland 7 20 C Palace 4
Van Persie rose unchallenged to guide home Wayne Rooney's 27th-minute corner to spark scenes of jubilation at Old Trafford and silence the taunts of the visiting fans.
On another amazing weekend, in which Chelsea's home draw on Saturday was followed within 24 hours by shock defeats for Tottenham and Manchester City, United have now closed to within five points of Arsenal, who suffered their first league defeat since the opening day of the season.
Indeed, six points now separate the first eight in the table, with Liverpool and Southampton now Arsenal's closest pursuers.
Man Utd 1 - 0 Arsenal Swansea 3 - 3 Stoke City Sunderland 1 - 0 Man City Tottenham 0 - 1 Newcastle
Loic Remy's early strike sealed a hard-fought 1-0 victory for Newcastle against Tottenham at White Hart Lane but it was goalkeeper Tim Krul who will deservedly take the plaudits.
With all of the pre-game talk about Spurs stopper Hugo Lloris missing out after being knocked unconscious at Everton last weekend, it was the Magpies' own number one who produced heroics to earn his side a win.
Remy's well-taken strike in the 13th minute - his seventh goal in his last seven Barclays Premier League appearances - put the visitors ahead before his Dutch team-mate took centre stage, blocking Spurs at every turn.
In Sunday's other game, Swansea suffered yet more stoppage-time agony as Charlie Adam's penalty earned Stoke a point in a thrilling 3-3 draw at the Liberty Stadium.
Jonathan Walters and Stephen Ireland gave the visitors the half-time advantage.
Wilfried Bony got one back early in the second half before Nathan Dyer levelled and the Ivorian struck his 10th goal of the season to put Swansea ahead with four minutes to go.
But Swansea, who had let leads slip in the dying moments of both Europa League meetings with Kuban Krasnodar, were denied again when referee Robert Madley decided Wayne Routledge had handled a Ryan Shawcross header and Adam made no mistake from the spot.