Eddie Jones felt England paid the price for ill-discipline and too many players having an off day as their Six Nations Grand Slam hopes went up in smoke in Wales.
Having beaten Ireland and France in their opening two fixtures, England fell to a 21-13 defeat in Cardiff as Wales maintained their own chances of completing the Slam.
Cory Hill and Josh Adams crossed in the second half to help complete a record 12th consecutive Test victory for Warren Gatland's side, who trailed 10-3 at the break with Tom Curry scoring for England.
And England coach Jones says his side fell short in the finer points of the game.
"It was one of those nip and tuck games and it's a game of small margins," he told BBC Sport.
"We let ourselves down in a couple of areas. They beat us in the air, the penalty count was strongly against us and that gives the opposition field position and the chance to score and that's what happened.
"It's a tough game and I don't know whether we lost our heads, but they put us under a lot of pressure. You're always going to get some tough calls away from home and that happened."
Captain Owen Farrell admitted he did not have his best game in an England jersey, but Jones says the team collectively did not hit top gear.
"I just think a few of our players were a bit off and that happens sometimes," he added.
"That's the great thing about rugby, you never know what will happen. Full credit to Wales they deserved the win and played very well."