Manchester United manager David Moyes has taken responsibility for his side's decline this season following the home defeat to rivals Manchester City.
A clinical double from Edin Dzeko helped Manchester City move second in the Premier League with a 3-0 win.
Premier League top 10
The reigning champions are seventh, 18 points adrift of leaders Chelsea after City inflicted United's sixth home league loss of the season.
"I am the one who picks the team," Moyes said. "I take responsibility and always will do. It is disappointing. I thought it would be a tough year but I hoped it would be more competitive."
United have now lost more home league games this season than the three previous campaigns combined.
Manchester City took the lead after 43 seconds at Old Trafford and never looked back, exposing United's soft centre almost at will with Dzeko and Yaya Toure netting in the second half to inflict another painful defeat on home boss David Moyes.
"It was an amazing game from the first to the last minute," striker Dzeko said on Sky Sports. "We wanted to start playing our game early, to press high and get an early goal which we did. After that it was all about us. We could have had another goal (in the first 10 minutes) but we scored two more in the second half."
Arsenal manager Arsene Wenger was, like United's Moyes, facing difficult questions after his side conceded a 90th-minute own-goal from Mathieu Flamini to draw with struggling visitors Swansea on the back of a 6-0 thrashing at London rivals Chelsea.
It looked like Arsenal would claim all three points when second-half goals within a minute from Lukas Podolski and Olivier Giroud cancelled out Wilfried Bony's opener.
Meanwhile, Everton made it four wins in a row to maintain their own push for Europe as they beat Newcastle United 3-0 away with England hopeful Ross Barkley, Belgium striker Romelu Lukaku and Leon Osman all on target.
Arsenal stay fourth on 63 points, two behind third-placed Liverpool who host Sunderland on Wednesday. Everton are up a place to fifth, six points behind Arsenal with a game in hand in the race for a top-four finish and Champions League football.