On an incredible afternoon of football at Selhurst Park, the Eagles responded late to clinch a 3-2 victory against Peterborough United to secure their spot in the play-offs against Brighton and condemn the Posh to relegation from the Championship.
The visitors looked to have secured their spot in the second tier as they lead Palace 2-1 with seven minutes to go, but late strikes from Kevin Phillips and Mile Jedinak won the game for the Eagles who can now look forward to a two-legged clash against the Seagulls.
Despite their whole season potentially riding on this game the Eagles didn't show any signs of nervousness and went very close to taking the lead in the 12th minute. A cross from the right by Yannick Bolasie was met by Damien Delaney but Bobby Olejnik clawed away his header. Delaney managed to flick the rebound into the path of Glenn Murray who looked destined to score but a superb block on the line by Grant McCann saw the ball deflect over the bar.
Six minutes later a superb save from Julian Speroni prevented the Eagles falling behind when the pace of Dwight Gayle caught Danny Gabbidon out and the striker found himself one-on-one with the keeper but the Argentinian got down low to push his shot away from the bottom corner.
With the stakes so high both sides were pushing forward to snatch the vital opening goal and Murray just missed the target when he arrived first to an in-swinging corner from Bolasie but his header flashed over the bar with Olejnik flapping, and Nathaniel Mendez-Laing dragged a shot wide after a neat-one on the edge of the Palace box.
Having slipped into the relegation zone due to results elsewhere, Posh gave themselves a lifeline when they took the lead on 27 minutes when Lee Tomlin picked the ball up on the left flank and took on the Eagles defence. After breaking away from three defenders he found himself on the edge of the area and sent a low shot back across goal which crept under Speroni and into the net.
Palace were shellshocked and Posh controlled the next phase of the game and were inches away from doubling their lead when Mendez-Laing flashed a cross across the box which evaded two Peterborough attackers by the length of a stud with the goal gaping, and Michael Bostwick drove straight at Speroni from 30 yards.
However the Eagles managed to grab an equaliser from the penalty spot just before half-time when Peterborough failed to clear a corner and Gabbidon was tripped by Gabriel Zakuani. Murray stepped up to drive the ball straight down the middle from 12 yards to register his 30th Championship goal of the season and more importantly put his side level again.
Getting a goal just before the break seemed to give the Eagles a huge lift and after the restart they once again began to take the game to their opponents. Owen Garvan saw a shot fizz wide of the target from 25 yards before Murray was again denied by a goal-line clearance when his turn and shot was hacked away by Tommy Rowe.
But on 63 minutes Palace fell behind once again despite being on top. Mendez-Laing received the ball on the right flank and cut inside between Mile Jedinak and Dean Moxey before firing a shot past Speroni to send the Posh bench and their large travelling support into hysteria.
And it was only a flying stop that prevented Posh from extending their lead when a McCann free-kick headed towards the top corner but the veteran keeper dived at full stretch to tip the ball over his crossbar.
With 10 minutes to go Murray then saw a volley loop over the crossbar after a deflected cross from Wilfried Zaha deflected into his path but the equaliser did arrive with eight minutes to go when substitute Stephen Dobbie's ball into the box fell at the feet of fellow replacement Kevin Phillips, and he wriggled free of the Posh defence to thump the ball into the top corner.
And it got even better for the Eagles who clinched the win and sent Peterborough down at the same time. A now-trademark dangerous Dobbie delivery into the area was glanced into the back of the net by Jedinak's head to secure the Eagles' spot in the play-offs and end their long wait for a victory just in time for the end of season spectacular.
Palace: Speroni, Ward, Delaney, Gabbidon, Moxey, Dikgacoi (Dobbie 75), Jedinak, Zaha, Bolasie (Phillips 67), Garvan (Williams 67), Murray. Subs: Price, Dobbie, Wilbraham, Ramage, Moritz.
Peterborough: Olejnik, Alcock, Zakuani, Bostwick, Tomlin, McCann, Rowe, Payne (Barnett 90), Pritchard (Knight-Percival 88), Gayle, Mendez-Laing. Subs: Day, Swanson, Little, McDonald, Ferdinand.