Crawley Town clinched one of their best ever results when they shocked second-placed Peterborough with a 2-0 away victory.
Reds collected a surprise but brilliantly earned three points through a goal in each half by Gary Alexander.
He struck in the 22nd and 64th minutes to prevent Peterborough extending their six-game winning runin wich they had scored 23 goals.
Crawley made a great start at the impressive London Road stadium with three early chances.
Nicky Adams seized upon some poor defending to get a shot in which was turned around for a corner by Bobby Olejnik.
Billy Clarke then fiorced Oljnik to get down low to keep out an attempt from the edge of the area.
Clarke then had another go in a great move put through from the left by Mat Sadler, again denied by the keeper.
Crawley continued their early pressure and thoroughly desevered to take the lead in the 22nd minute when Adams crossed to Alexander on the right who volleyed into the net from the narrowest of angles.
Peterborough had been quiet so far and created their first chance when Lee Tomlin struck a free-kick for Britt Assombalonga to head on target but the ball was safely caught by Reds’ keeper Paul Jones.
Crawley then dominated the exhanges before half-time with Andy Drury nearly setting up Alexander for a second but ball went across the face of goal.
Clarke then played one through to Alexander in a break through the middle but the pass was overhit.
Peterborough made two substitutions at half-time with Danny Swanson replacing Lee Tomlin and Mark Little coming on for Kgosi Ntlhe.
The changes had an immediate effect as Posh put pressure on the Crawley goal after the break as Little twice forced Paul Jones into action in a few minutes.
But it wasn’t long before Crawley were again pressing forward as Adams linked up well with Drury before the former Ispwich midfielder blasted wide.
Reds fans then sensed a possible superb three away points as the ball was played in toward Alexander who met the ball perfectly in the 64th minute with his left foot to put away his and Reds’ second goal.
Joe Walsh tested Olejnik again with a header as the visitors kept Peterborough on the back foot.
Craig Alcock supplied Tyrone Barnett in the box only for the former Broadfield Stadium favourite to header over the bar.
Clarke saw an audiacious lob fly narrowly over the bar from 45 yards after robbing a defender.
Crawley had to play out the last three minutes plus six minutes of injury-time with only ten men after Mike Jones was sent off for his second yellow card given for kicking the ball away.
Posh had a penalty appeal turned down just before the end as McFadzean brought down Assombalonga.
Crawley fielded an unchanged side from the one which narrowly lost 2-1 at Wolves last Friday.
The only change was on the bench with new signing Emile Sinclair - who joined from Peterborough on Thursday - making his debut in place of Connor Essam.
Peterborough made four changes to the side which had thrashed Reading 6-0 in the Capital One Cup in midweek, but just one from that which beat Tranmere 5-0 in their last League 1 match.
Gabriel Zakuani came in for Nathaniel Mendez-Laing.
Former Reds Michael Bostwick and Tyrone Barnett lined up for Posh against their former side, while Paul Jones and Josh Simpson did likewise for Crawley.
REDS: Paul Jones, Mat Sadler, Kyle McFadzean, Joe Walsh, Josh Simpson, Andy Drury, Dannie Bulman, Mike Jones, Nicky Adams (James Hurst 85), Gary Alexander (Jamie Proctor 77), Billy Clarke (Connolly 90)
Subs: Jonathan Maddison, James, Hurst, Mark Connolly, Sergio Torres, Jamie Proctor, Luke Rooney, Emile Sinclair
POSH: Bobby Olejnik, Craig Alcock, Kgosi Ntlhe (Mark Little 46), Gabriel Zakuani, Michael Bostwick, Britt Assombalonga, Lee Tomlin (Danny Swanson 46) , Grant McCann, Tommy Rowe, Danny Kearns (Nathaniel Mendez-Laing 64), Tyrone Barnett
Unused Subs: Joe day, Jack Payne, Nathaniel Knight-Percival, Jaanai Gordon
Referee: D Bond