England captain Michael Vaughan admitted that his side failed to take their chances after a seven-wicket defeat to Australia in Antigua.
Australia cruised to 248-3 after England had been dismissed for 247.
Vaughan said: "Kevin Pietersen's 100 was a fantastic knock, but the rest of us didn't play well enough around him for us to get to the 280 we needed.
"We're certainly making it difficult for ourselves - we need to win our last three games now to get into the semis."
Vaughan himself was dismissed for just five and England's batsmen failed to build on a third-wicket partnership of 140 between Pietersen (104) and Ian Bell (77).
From 164-2 in the 30th over - when a score of 300 looked on the cards - they were choked by Australia's seam bowlers late on and only one other batsman, Ravi Bopara, reached double figures.
We were squeezing them quite effectively around the 20th over of their innings
Vaughan said: "There aren't that many of us batsmen playing that well at the moment. Personally I'll keep fighting, and hopefully I'll get some runs against Bangladesh on Wednesday.
"Around the 30th over we were 160-odd for two, and at that stage we looked like we could post 280 or 290. That would have been a really competitive total on this pitch.
"We were squeezing them quite effectively around the 20th over of their innings, and that was the area of the game where we could have won it.
"But Ricky Ponting and Michael Clarke played great innings - all credit to them.
"We're a squeezing attack, and we usually get opportunities to get wickets at the top when the ball swings, but it didn't happen for us today."
Prince Harry was a disappointed observer in Antigua
Vaughan played down an incident when Kevin Pietersen caught Andrew Symonds on the boundary edge in the 42nd over, and took five paces before throwing the ball away as he stumbled over the rope.
England queried the decision to give Symonds not out, but Vaughan said: "Being honest, it wasn't an option to give him out. We were clutching at sraws at that stage."
The team must now regroup quickly for a game against Bangladesh after back to back defeats by Sri Lanka and Australia.
"It's very frustrating. We got to bed the other night, thinking we should have won that game and we know we were in a great position to put Australia under more pressure today.
"We are very, very close to being a really good one-day team. We are just not winning critical periods and doing enough during the whole match," Vaughan added.