Eddie Howe took the blame for Newcastle's dismal away form after their winless run on the road in the Premier League extended to nine matches with a 3-1 defeat against Brentford on Sunday.
Howe's side took the lead when Harvey Barnes scored his 50th Premier League goal in the 27th minute at the Gtech Community Stadium.
But the Magpies collapsed in the second half as Kevin Schade equalised in the 56th minute after Newcastle keeper Nick Pope missed a flick-on at Michael Kayode's long throw.
Newcastle defender Dan Burn was sent off for a second booking when he conceded a penalty with a foul on Dango Ouattara in the 73rd minute.
Igor Thiago converted the spot-kick and the Brazilian forward netted again in stoppage time to leave Howe in despair on the fourth anniversary of his appointment.
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"I'm very disappointed that we got ourselves in a good position again and weren't able to capitalise on that," said Howe, whose team also lost 3-1 at struggling West Ham last weekend.
"It was always going to be a tough, physical game, and we needed to stand up to that.
"One mistake in the build-up to their first goal, we needed a reaction to that, and we didn't get it. Very frustrating end to the game."
Newcastle are languishing in 14th place, just two points above the relegation zone.
In contrast to their strong form at home this season, Howe's men have looked timid on their travels.
Insisting it was his responsibility to resolve the problem, Howe said: "It's different to the West Ham game. It's important today that I support the players.
"We know it's not good enough and I take full responsibility for that, and if we want to get that right it starts now and that's all that I can do at this moment."