Manager Russell Martin slammed an unacceptable display after Swansea let an early lead slip in a 3-1 defeat at Preston.
Joel Piroe's neat finish put Martin's men ahead in the 19th minute but their advantage was quickly cancelled out by Liverpool loanee Sepp van den Berg.
Emil Riis gave North End the lead in the dying seconds of the first half before Ben Whiteman's 52nd-minute free-kick settled the outcome.
The Swans have now lost three of Martin's first five league games in charge and the new boss admitted the manner of this defeat was particularly painful.
He said: "I am really disappointed and didn't see it coming.
"We scored a goal of real high quality but to let them score so soon is unforgivable. The goals we have conceded have really hurt me.
"When you go 1-0 up it is a chance to establish some control and the opposite has happened.
"We did not look after the ball well enough and were not aggressive enough to defend our box.
"I said to the lads that if we lose in our way, I am ok with that. Today is not a way I can accept losing."
The visitors started on top at Deepdale with Piroe heading over Ethan Laird's cross inside the first two minutes.
The Dutch striker was then on hand to convert Liam Cullen's incisive pass to break the deadlock but van den Berg popped up at the back post to level from Josh Earl's deep cross just two minutes later.
Preston dominated thereafter and Riis saw a couple of efforts kept out by Steven Benda before eventually getting the better of the goalkeeper just before the break, smashing home Sean Maguire's cross.
When Benda brought down Riis outside the box shortly after the restart, Whiteman stepped up to find the bottom corner and consign the toothless Swans to defeat.
Martin added: "It is a game too many, mentally and physically, for a lot of the guys.
"There were a lot of tired bodies. The only positive for me is that we will never be weaker than that in terms of squad selection.
"It has been a hectic four weeks with no real time on the training field.
"We have got some time to work on the training pitch now and we will be a very different team in two weeks."
North End boss Frankie McAvoy was understandably pleased after seeing his side record their third win in the space of a week, hailing a 'magic' response to going behind.
He said: "Once we got the press right, we started to make things happen.
"After they scored, I have to credit the players, I thought they were excellent in terms of harassing and making it difficult for Swansea to play.
"I thought the response of the players was magic. I just felt how we pressed and harassed in the second half was excellent, it is everything we have worked on.
"We created a number of chances and I don't think we really gave Swansea many opportunities in the second half, so as a coach I was delighted with that.
"We worked really hard on trying to win the ball as high up the pitch as we could and we felt we had a threat."
