Louis Van Gaal slammed Manchester United's worst display under his management and accused his players of failing to follow his gameplan in their 3-0 loss at Arsenal.
United headed into Sunday's match at the Emirates Stadium with ambitions of returning to the Premier League summit at the expense of rivals Manchester City but they suffered a horrific start.
Alexis Sanchez and Mesut Ozil scored within 74 second of one another to make it 2-0 after seven minutes and the contest was as good as over when Sanchez capitalised on further generous defending to rifle home a third in the 19th minute.
United dominated possession after the break but failed to cause the Arsenal backline much cause for concern, ensuring they slipped to third in the table behind their opponents on goal difference.
Van Gaal told Sky Sports: "When you start like that you can never win a game.
"We lost every duel, every second ball, were not tight on their midfielder and they can play. They are a fantastic team, when you give them that space it is difficult.
"That was the worst United have been under me, we were not able to give a normal performance.
"I have never seen that of my team, that is the question I put to my players. You cannot solve that now - a lot of emotion and I am emotional as well.
"I could not change anything, if it was just one player then I can take measure but it was more than half of my team who were not doing what we had agreed in our gameplan.
"I am shocked, you don't expect it, we were top of the league, won our last four matches and have to protect our position against Arsenal.
"The way we had started, so without emotion. I did not expect that, it is difficult to understand and I will have to look for the reasons."
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.