Chris Coleman fumed at his 'soft' Sunderland side for gifting Cardiff City the initiative just seconds into the second half.
Callum Paterson scored from a corner to put the Bluebirds ahead, sparking a collapse from the opponents who saw Didier Ndong sent off and Joe Ralls score a second within ten minutes.
Cardiff strolled to a 4-0 win after that, with Paterson scoring again and substitute Anthony Pilkington converting at the back post with the last kick of the game.
Coleman said: "The first goal, 45 seconds after the restart, you can't accept it. For 45 minutes we’re OK, our keeper only really has save to make in the half. To then give them a goal like that, you can’t. Well, you can, but if we do we will stay exactly where we are.
"We’ve got 900 fans down here who have been travelling since three this morning, that is tough. Bottom of the league, it is a long journey home for them. We didn’t deserve anything after that 45 seconds. I can’t get my head around it. What are we thinking? We’re fine, we’re set, to let that happen… I can’t accept that."
It was a similar goal to the crucial header from Ethan Pinnock in the recent home defeat to Barnsley. The centre-back stooped to head the Tykes home unmarked from a corner shortly after the restart, a moment from which Sunderland did not recover.
The similarity was not lost on Coleman who said his side were showing a 'soft mentality'.
He said: "45 seconds after the restart, 1-0 down, you can’t accept that. It’s a poor mistake we made. You can’t do that at this level, not when you are we are.
"It’s soft, a soft mentality, simple as that, no toughness. Toughness isn’t nailing someone in a challenge, putting them on their backs, that is easy. Toughness is mental, that’s what it is.
"Staying strong, making consistently good decisions. We’re going to stay where we are doing that, it’s no coincidence we're at the bottom. We’re gifting goals to teams."