Blackpool goalkeeper Matt Gilks produced a brilliant display as the Seasiders burst Newcastle's bubble with a 2-0 victory at St James' Park.
Adam then produced the pass from which DJ Campbell sealed the win in the 90th minute, but only after keeper Gilks had produced a string of superb saves to deny Newcastle an equaliser.
Gilks, who had kept out Kevin Nolan's first-half effort, frustrated Joey Barton, substitute Peter Lovenkrands and Andy Carroll as the Magpies staged a committed fightback in front of a crowd of 49,597.
The defeat, Newcastle's first on their own turf in 27 attempts, served as a reminder to Chris Hughton's men, if they needed one, that their 6-0 victory over Aston Villa in the last fixture at St James' Park, was a start and nothing more.
Five months ago, Blackpool had arrived on Tyneside as one of the few sides to have beaten the Magpies in the Championship, and left on the wrong end of a 4-1 beating which was every bit as comprehensive as the scoreline suggests.
They returned to the north-east knowing that Villa had also been sent packing as Newcastle romped to a stunning victory 24 hours after they had lost by the same score at Arsenal.
But there was a determination about Ian Holloway's men from the off that they would not be blown away, and when referee Lee Mason sounded the half-time whistle, few inside St James' could have argued they were value for their 1-0 lead.
Had it not have been for a superb double save by Harper, their lead might have been even bigger.
The home defence was carved open by Adam's 12th-minute through-ball and the keeper had to block Campbell's effort at point blank range before turning Brett Ormerod's follow-up around the post.
Newcastle's response was swift and wingers Wayne Routledge and Jonas Gutierrez took up the gauntlet, but it was defender Mike Williamson who came closest to giving them the lead.
He met Barton's 25th-minute free-kick with a looping header which evaded Gilks' dive, but came back off the post.
Gilks did intervene, however, seven minutes later when he won a one-one-on duel with Nolan after the midfielder had run on to Carroll's flick-on.
But just as it looked as though the home side were ready to reply they were caught by a sucker punch on the stroke of half-time.
They looked to have enough men back to cover Luke Varney's surge into the box, but Alan Smith's challenge was untidy and when the midfielder went down, the referee pointed to the spot.
Adam beat Harper with the minimum of fuss and then unveiled a T-shirt bearing the message "4 Parky".
Blackpool started the second half in positive mood, but were almost caught within six minutes when Nolan helped the ball on for Carroll.
The striker attempted to round Gilks, but the keeper managed to grab the ball in the nick of time to deny him.
Holloway's men were gradually retreating as the home side started to mount a concerted onslaught.
But for all their possession, Newcastle were able to create little in the way of clear-cut chances with Carroll, Fabricio Coloccini and Williamson all coming close to meeting Barton's 59th-minute free-kick, but not close enough.
Gilks had to come to the rescue three minutes later when Barton muscled his way into the box and looked certain to score until the keeper threw out a hand and Nolan saw a 68th-minute volley partially blocked.
Hughton handed a debut to France international Hatem Ben Arfa in place of Jonas.
Time was running out fast and the tension grew as Lovenkrands fired straight at Gilks, who then collected Carroll's looping header before seeing Jose Enrique shoot wildly over after cutting into the box.
Gilks preserved his side's lead once again with 12 minutes remaining when, after Carroll had played Lovenkrands through, he got down well to palm away his firm drive.
However, he saved the best for last when he blocked Carroll's goal-bound shot with his foot two minutes from time.
Newcastle's despair was complete at the death when, as they pushed men forward, they were caught on the break as Adam found Campbell and he fired unerringly across Harper and into the bottom corner.
