Steven Taylor scored a late winner for Newcastle to deepen Sheffield United's relegation worries.
Taylor made no mistake with his header
The defender was first to James Milner's curling right-wing corner and powered in a header from eight yards.
The Magpies were the better side and took the lead through Obafemi Martins who fired in a low volley from Milner's lay-off early in the first half.
Substitute Christian Nade equalised for the Blades with a close-range effort, before Taylor's late strike.
The defeat leaves the Blades treading water in the relegation zone, with must-win matches against fellow strugglers West Ham and Charlton to come in the next two weeks along with a daunting trip to Old Trafford.
In the past, the visit of Newcastle would have been met with some trepidation, but the Magpies themselves were coming into the game having not scored in five of their last six games and having picked up just four points from 18.
However, a jittery-looking Blades did not get going in the match until the second half and by that time Newcastle had taken a deserved lead through the constant menace that was Martins.
The Nigerian's pace troubled the Yorkshire outfit all match but it was his calmness under pressure that gave Glenn Roeder's men an early advantage.
A cross from the equally effervescent Duff found Milner who nodded down for Martins to volley in from 12 yards.
Duff had chances to get his name on the scoresheet, but smashed an effort into the side-netting when put clean through before driving a shot a yard wide of Paddy Kenny's right-hand post.
Martins was also a fraction away from adding his second with a bit of opportunism that saw him get to ball before Kenny outside the area and curl in a shot that rebounded off the post to Antoine Sibierski who blazed ridiculously over.
Neil Warnock's men, who did have a 10-point gap above the relegation zone, also had their chances and posed many more problems for the Newcastle defence in the second half, delivering a handful of difficult balls into the area from all areas of the pitch.
Michael Tonge came close to converting one of those but he blazed over from just eight yards.
But the home side were given hope when substitute Christian Nade slid in the equaliser after Nick Montgomery laid the ball into the striker's path after collecting Keith Gillespie's beautifully-flighted cross.
However, that joy though was short-lived when Taylor thumped home a header from Milner's teasing corner.
And Newcastle had Shay Given to thank for keeping the scores at 2-1 when deep into injury time he palmed away a goalbound Danny Webber shot from the edge of the six-yard area.
Sheff Utd boss Neil Warnock:
"I am distraught but I have to keep my chin up.
"We had some great chances but we gave away two elementary goals and we got punished because of that.
"They've not had to work hard for the win. When we equalised I didnt expect them to score a goal from a corner. But the Premiership is so unpredictable."
Newcastle boss Glenn Roeder:
"If people are honest with themselves they did not expect that to happen today.
"I believe it was only inside our dressing room that we believed we could come here and win.
"People have looked at us and thought, at times away from home, we're not hard enough. That gave them the motivation to come out fighting."
Sheff Utd: Kenny, Bromby, Lucketti, Jagielka, Armstrong, Gillespie, Montgomery, Leigertwood (Tonge 56), Stephen Quinn (Nade 56), Kazim-Richards, Stead (Webber 87).
Subs Not Used: Morgan, Geary.
Goals: Nade 74.
Newcastle: Given, Solano (Onyewu 84), Moore, Taylor, Carr, Milner, Butt, Parker (Emre 56), Duff, Sibierski (Dyer 75), Martins.
Subs Not Used: Harper, Babayaro.
Goals: Martins 17, Taylor 80.
Ref: M Halsey (Lancashire).