The Eagles took an early lead at Cardiff City Stadium when Australian midfielder Jedinak headed home inside four minutes of kick-off and it looked it may be a good day for Ian Holloway and his men.
However, Malky Mackay's Bluebirds hit back through Craig Noone a minute before the break prior to substitute Aron Gunnarsson's 73rd minute winner.
The defeat forced Palace down to fourth place on the table and extended their winless run to four matches whilst Cardiff went five points clear of second-placed Hull City.
Jedinak's goal, which stunned the sellout crowd, was just his second of the campaign after the opener in the 2-2 draw with Millwall in October. He has now scored just three league goals in 54 appearances since joining Palace from Genclerbirligi in July 2011.