Javi Gracia admitted Leeds were “very bad, “soft” and lacking “aggression” as they conceded five at home in the top flight for the first time in 32 years.
The Leeds coach saw his side throw away a first half lead from Patrick Bamford, to leak five in 32 minutes including two from Crystal Palace forward Jordan Ayew.
It was their joint heaviest defeat at Elland Road and Gracia said: “I cannot explain it after a good first half. We have to be really disappointed because the second half was very bad, the result as well is difficult to accept.
“We were not aggressive, and soft. After that it is difficult to defend. We have to learn something. When we are 100 percent we can beat anyone. If we don’t we know what can happen.”
Thousands of fans walked out of Elland Road and there were boos at the final whistle, after a result that deepens Leeds’ relegation worries. They face Liverpool next.
Gracia added: "It's unbelievable after that first half we had to finish like that. We dominated the first half and created many chances. We could have finished the game. After we conceded before half-time everything changed. We started very bad in the second half and didn't perform as well.
"There's only one way, to work hard and try to understand why we conceded this result and to try to come back and do all the things we've been doing well.
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"We try to work hard this week to give the fans a better performance and result.
"When we conceded the second goal, Palace played really well with the spaces. They have very good players to run, to counter and to defend. Palace were really tough for us.
“It's only a game. We try to keep a positive mentality for the next game.”
Sunday's result means Leeds sit just two points and two places above the relegation zone with eight games remaining.
