Captain Waqar Younis could not conceal his distress after Pakistan were humbled by England in Cape Town.
The loss leaves Pakistan's hopes of progressing to the next stage of the tournament hanging by a thread.
"Of course it is very disappointing," Waqar said.
"Our performance today was very poor."
Pakistan, who were forced to bat under lights after losing a vital toss, had no answer to the inspired swing bowling of 20-year-old James Anderson.
The collapse came a day after Waqar had predicted England's attack would be their weakest link in the match.
"The ball was swinging a bit more and full credit to England - they did well," Waqar said.
"Especially Anderson, who I thought bowled an excellent spell."
Pakistan can expect to take full points from the next match against Holland on Tuesday.
But their match against India on 1 March now looms as a do-or-die clash for them.
"That is a very important game and it will decide where we stand," he said.
"We have still got three more games.
"We have got to make
sure we put our heads together and come back hard again."