Newcastle head coach Steve Bruce compared his side's defending to "something you see on a park on a Sunday" after they conceded three times in the last 13 minutes to lose 5-2 at Leeds.
Having seen off Crystal Palace and West Brom this month, the Magpies were chasing a third successive win for the first time since November 2018 but they imploded in the closing stages at Elland Road.
Ciaran Clark had headed them level, exposing Leeds' set-piece fragilities, but Newcastle midfielder Sean Longstaff dithered on the ball in his own area, leading to Stuart Dallas putting the hosts ahead again after 77 minutes.
The visitors were then caught twice on the counter in the last five minutes as Ezgjan Alioski finished well before Jack Harrison spectacularly found the top corner from 25 yards, much to the chagrin of Bruce.
"Up until 75 minutes I thought we were comfortable. I thought we looked a threat when we equalised," he said.
"Of course Leeds are always going to ask you questions the way they play, they do it very well, but we've gifted them the two or three goals at the end. Unfortunately they're something which you see on a park on a Sunday.
"We can't make those mistakes we've made here. The third goal in particular where we gave the ball away cheaply in our own box. You get punished for things like that at this level.
"At the wrong time we've given away poor goals, not defended well enough and got punished. It's unacceptable."
Bruce refused to hide behind Newcastle's recent coronavirus crisis, with several of his players still unavailable after contracting the disease, although he feels his side were denied a clear penalty with the score at 1-1.
Leeds captain Liam Cooper came through the back of Callum Wilson, seeming to make no contact with the ball, and even though the incident was checked by the video assistant referee, no spot-kick was given.
Bruce said: "I honestly was all for VAR when they brought it in to make sure the clear and obvious mistakes that the referee misses, that's what the VAR is there for.
"If anybody looks at the challenge you understand that it's a clear penalty. We might not have gone on to win the match but certainly when you take the lead in the Premier League then the outcome could be very, very different.
"I'll leave it to other people to judge."
Leeds fell behind when Jeff Hendrick put the finishing touch to Wilson's flick-on from the fit-again Ryan Fraser's cross, but headers from Patrick Bamford and Rodrigo put Leeds ahead.
Clark headed home from a corner to level matters but the hosts were well worth their win after a barnstorming finish as they leapt above their opponents and moved up to 13th in the Premier League.
Leeds head coach Marcelo Bielsa said: "It was a deserved victory. In both halves we attacked a lot and created plenty of chances but in the second half we were more efficient.
"The team carried on playing in a calm and organised manner after they levelled the game and eventually we were able to get on top of them again and get on top of them when we needed to."
After beating Newcastle at home for the first time since September 1999, Leeds now turn their attention to Sunday and a trip to Old Trafford to take on old rivals Manchester United.
Having drawn a line under back-to-back defeats to Chelsea and West Ham, Bielsa added: "Winning is always a positive thing and it helps you to go into the next game calmer."
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