Nahki Wells and Huddersfield missed the chance to put the pressure on Newcastle after they were held to a 1-1 draw at Derby - confirming Brighton's promotion to the Premier League.
Former Huddersfield midfielder Jacob Butterfield levelled with two minutes to go to finally break the spirited Huddersfield defence.
Huddersfield had led since Collin Quaner's strike in the ninth minute but Butterfield, who played 50 times for the Yorkshiremen in the 2014-15 season, rifled an unstoppable effort past Danny Ward on 88 minutes.
Huddersfield, who registered just one shot on goal, had defended resolutely throughout to frustrate the Derby.
The draw leaves Huddersfield seven points behind Newcastle with a game in hand and five points inside the play-off places. They also cannot catch leaders Brighton, who beat Wigan earlier in the day.
Rai Simons and his Chesterfield teammates were relegated to Sky Bet League Two as they went down with a whimper in a 3-1 defeat at Scunthorpe.
Scunthrope dominated the game from start to finish, controlling possession and territory to secure themselves a top-six finish.
They took the lead in the 21st minute via Paul McGinn's own goal. He headed into his own net after Josh Morris' corner had been flicked on at the near post by Neal Bishop.
Simons who started the match was replaced in the 24th minute with an injury.
Scunthorpe added a second goal eight minutes before the break, Ivan Toney leaping like the proverbial salmon to beat goalkeeper Thorsten Stuckmann to Bishop's looping cross and nod home.
Stuckmann came to the away side's rescue when denying Paddy Madden and a cracking curler from Stephen Dawson, he could not keep out another clumsy goal when Toney bagged his second in the 73rd minute.
Tom Anderson headed in a consolation goal in stoppage time, but by then Chesterfield’s fate was sealed.
Jabo Ibehre's third goal in as many games rescued a point for Carlisle in a 1-1 draw with play-off rivals Stevenage.
Reggie Lambe started the match before being substituted in the 67th minute.
Stevenage took the lead shortly after half-time through a Steven Schumacher penalty and soaked up plenty of pressure as they preserved their two-point advantage over the Cumbrians in League Two despite Ibehre's second-half equaliser.
Carlisle dominated the early exchanges and skipper Danny Grainger wasn't far away with a 25-yarder that whistled over the bar.
Despite having shown comparatively little as an attacking force up to the 50th minute, it was Stevenage who went in front from a penalty following a clumsy challenge on Kgosi Ntlhe, leaving Schumacher to smash the ball high into the net.