Manchester United captain Nemanja Vidic admitted he felt 'horrible' after the Red Devils' 4-1 defeat at the hands of arch-rivals Manchester City.
The Premier League champions were blown away by first half goals by Sergio Aguero and Yaya Toure.
Manchester United nemesis Aguero added a third shortly after the interval before Samir Nasri completed the rout with a 50th-minute volley.
Wayne Rooney managed to score a wonderful free-kick with three minutes to go but it was merely a consolation goal for David Moyes' side.
Vidic, speaking to Sky Sports, said on his side's embarrassing loss at the Etihad Stadium: “To lose a derby game is horrible.
“It's more difficult when you lose the game after this kind of performance.
“We were 4-0 down and it was really tough. We were never close to winning the game or even getting a draw.
"It's disappointing but we have to come back. We're down now but from tomorrow we'll try to be positive and win the next game and move on."
The defeat means United have won just two of their opening five Premier League games.
Moyes is likely to ring the changes for his side's midweek Capital One Cup match against Liverpool at Old Trafford with fringe players Jonny Evans, Wilfried Zaha and Javier Hernandez all likely to start Wednesday's encounter.
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