"It was a very, very frustrating game and at the end of the day you don't win any match if you make errors like we did on Sunday," he says.
"Even with the spirited revival and possibly the deserved equaliser, you can't get away with what we did in any league.
"If you analyse the game we actually played reasonably well going forward, even in the first half, and we were a lot brighter and sharper in everything we did.
"But making mistakes such as we did it is like sticking a pin into a balloon - everything goes out of you.
"Leeds are obviously having a bit of a tough time and when we went forward they looked vulnerable - but Manchester United will have more quality, even if they are going through a sticky patch themselves.
"They are one of, if not the best, sides in the country and it is going to be a really tough one this Sunday."
Paul says the errors must be cut out on Sunday and adds:
"We equalised and then nearly made it 2-1 - but then we handed them the chance to go in front and it was so deflating.
"The second goal was a disappointment because we spend a lot of time on the arrangement of set pieces and corners, and there are set rules that players didn't adhere to.
"The third goal was a scrappy affair but we poorly defended the corner and as a result Kewell has hit the volley that went in.
"Then there was the back pass from Christian where he didn't see Viduka - it was just an individual error.
"We don't spend hours and hours on attacking during the week because we are a team with players that can produce moments of inspiration and quality, so that takes care of itself a little bit.
"But defending set pieces is certainly something we work upon and that is what makes it frustrating.
"There were a lot of experienced players out there on Sunday, but it was evident that we had a massive problem.
"The pleasing thing was that we looked like a threat going forward again - but you just cannot make those mistakes.
"The fans have been fine as far as I am concerned and they have not seen the best of us by any means; they have been as frustrated as anyone and have got the right to voice their opinions.
"There is no way that the defending was good enough on Sunday in the first half but they got right behind us in the second half and trying to get that fourth goal to go in.
"There were real good chances to equalise and we probably created as much in that second half as we did in the last three home games.
"Ian Pearce, Joe, Jermain with his head, Paolo with his head...great chances.
"I think David only had one shot to save in the second half and that just shows you how well we did in pinning them back - and if we had got the fourth goal we might have got the fifth."
Paul was delighted at the return of Trevor Sinclair and Paolo Di Canio against Leeds and adds:
"They are quality and both took enormous credit out of the game; Paolo was superb and Trevor deserves enormous praise for playing just six days after an operation - and he obviously scored a great goal with his head as well.
"He came in on Saturday and was initially a little bit unsure; he came out with the fitness people at first and then got involved with the full training.
"Towards the end of the session you could see he had grown in confidence and after a chat it was clear he felt more positive about it.
"Paolo loves to play football; he has a great knowledge and passion for the game and wants to be involved with good play and good teams.
"He will keep that going until his dying days and I thought he was excellent on Sunday."
As for that pre-match 'huddle' on the pitch before the Leeds game, he says:
"I wasn't aware of it but it was something the players had talked about; there is nothing wrong with everyone getting together and fighting for the cause.
"But it was a case of shutting the stable door after the horse has bolted on Sunday; you can't give a team in the Premiership a three goal start."
Paul says that Sebastien Schemmel's contribution was an important one and says:
"It was very difficult to come on in that situation but we pushed them back in the second half and dictated the tempo of the play."
But he is also quick to defend the man Sebastien replaced, Tomas Repka, who had been booked in the first half.
Amongst the scurrilous nonsense written about him this week was one newspaper claiming the West Ham fans were taunting him for being fat - when it was clear the chants were directed at Mark Viduka, who was booked with him.
"Anyone who saw him play last year knows that he was one of the reasons we were so resolute last year; him and Christian were so strong for us, and we know what he can do," he says.
"I haven't any doubt about anyone's commitment and certainly not Tomas'; it is just a case of how it is controlled.
"He is a very aggressive player and when he channels it correctly that is fine; you don't play in Serie A for the amount of time he did if you are not a good player.
"But you can't let emotions get the better of concentration because you can lose your way."
As for the team putting things right on Sunday and preparations for the game, he says:
"There has been a lot of hard work; there is no way around it, you get on the training field and work your socks off, and there have been a few corners and free kicks flying around this week, I can tell you.
"There has also been a lot of discussion on how to defend."