Palace came from a goal behind at Selhurst Park to claim an important victory in their bid for Championship survival with a 3-1 win over Preston.
The first goal of the game came somewhat against the run of play after Palace had created three good chances in the opening stages.
In the first minute Stern John had certain sections of the crowd celebrating when his looped effort made the net ripple, but they died out soon after when it became clear the ball had not dipped enough and had dropped onto the roof of the net.
A minute later Sean Scannell was put through on goal by a clever flick from John. As the youngster closed in on goal Tom Williams managed to catch him up and put him under pressure, forcing him to slide as he shot and the ball ran wide.
Palace thought they had taken the lead on eight minutes when an Ambrose corner was met by Paddy McCarthy with a thumping header to the top corner, but Neil Mellor was well placed to clear it off the line.
The ball came back to Derry in the midfield, but he took too long with it and was robbed by Paul Coutts who broke with two in support against Matt Lawrence as the last man.
He then played in Treacy who slipped the ball calmly under Speroni after he had raced out to the edge of his box to close down the angle.
Palace rallied and continued to create good chances that deserved reward.
On 14 minutes Johnny Ertl crossed into the middle of the box where Ambrose was well placed to hit it first time, but he scuffed his shot and Lonergan was able to make the save.
The Preston keeper excelled himself though moments later when he acrobatically denied Calvin Andrew after the striker had met a corner with a powerful header from ten yards out.
The visitors should have extended their lead on 26 minutes when Jon Parkin fired over from 12 yards out. The towering centre forward was picked out by Mellor with a knock down, and the former Hull City striker took a touch to give him the space and then shot wastefully over with the goal gaping.
Palace's work finally paid off with five minutes to go of the half. Calvin Andrew's cross was not cleared properly by the Preston defence and Scannell cleverly headed the ball back into the path of Danns who, from inside the six yard box, stayed calm to slot the ball past Lonergan.
The home side then had a late penalty appeal turned down when the ball hit the hand of Elliott Ward inside the area but Mr East waved away the appeals.
Preston began the second half strongly as Williams curled an early free kick over the bar and then Parkin saw his header blocked by McCarthy.
But it was Palace who got the all important third goal of the game on 51 minutes.
Danns broke down the left, squared up his marker before playing the ball across to Ambrose. It looked to have been cut out by a desperate lunge from a Preston defender but it squirmed beneath him and found its intended target.
Ambrose had the time to take a touch and fire an unstoppable drive in off the underside of the bar.
He almost turned architect moments later when a superb ball over the top put Andrew clean through, but he took too long on the ball and allowed Lonergan to close down the angle and smother the shot.
Some patient build up from Preston could have resulted in a lot more on 66 minutes had Treacy realised the amount of time at his disposal. The goalscorer was allowed to turn into acres of space between the Palace midfield and defence and opted to fire from distance with an effort that was always rising.
It was the same scenario for Matthew James minutes later as Palace began to defend deeper and deeper when he was able to turn 20 yards out and get a shot away without much pressure. Fortunately for Palace the midfielder screwed it horribly wide.
Hearts were in mouths on 80 minutes when James received the ball 20 yards out and curled a left footed effort to the top corner. It seemed to take an eternity as his looping effort beat Speroni at full stretch and dropped just over the bar.
But the win was made certain six minutes from time as a high ball into the box was spilled by Lonergan and fell to Andrew who had the simplest of finishes to seal it for Palace.
Preston threatened late on through Treacy who forced a tremendous save from Speroni with a curling free kick 20 yards out, but Palace closed out the remaining minutes to claim all three points.
Att: 16, 642
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Crystal Palace: 1. Julian Speroni, 3. Clint Hill, 4. Shaun Derry, 5. Patrick McCarthy, 7. Darren Ambrose, 8. Neil Danns, 9. Stern John, 14. Sean Scannell (10. Nick Carle, 85), 17. Matt Lawrence, 18. Calvin Andrew, 22. Johannes Ertl
Preston N.E: 1. Andy Lonergan, 11. Darren Carter (3. Callum Davidson, 66), 12. Shaun St. Ledger, 15. Paul Coutts, 16. Keith Treacy, 19. Billy Jones, 20. Tom Williams (9. Chris Brown , 80), 23. Matthew James, 24. Elliott Ward, 26. Jon Parkin, 33. Neil Mellor
Subs: 2. Michael Hart, 4. Richard Chaplow 14. Liam Chilvers, 22. Wayne Henderson, 34. Adam Barton