The hosts had kept clean sheets in their previous eight home games and looked well on their way to a vital win in their battle against relegation after first-half goals from Darren Ambrose and Neil Danns in Saturday's Championship encounter.
But Reading hit back before the break through Shane Long's penalty, as Julian Speroni was beaten on home turf for the first time in more than 13 hours.
And much like the buses around this part of south London, you wait ages for one goal and three come along at once.
After Ambrose had seen a penalty saved by Alex McCarthy, Jimmy Kebe crashed in an equaliser for Reading.
Substitute Jermaine Easter put Palace back in front but Noel Hunt's header secured a point for the play-off chasing Royals.
In a breakneck start, Reading were caught cold with just 39 seconds on the clock, Ambrose jinking along the edge of the penalty area before tucking the ball inside McCarthy's left-hand post.
Palace could have been out of sight in the first 15 minutes but Danns' lob was scooped out from under the crossbar by McCarthy, with referee Anthony Bates waving away protests claiming the ball had crossed the line, before Ambrose volleyed Steffen Iversen's cross wide.
Reading eventually woke up after a quarter of an hour and suddenly Speroni's goal was leading a charmed life.
In keeping out Jay Tabb's looping effort, Speroni spilled the ball at the feet of Hunt only for the Reading striker to take an air shot two yards from goal.
Instead, it was Palace who grabbed the game's second goal when James Vaughan robbed Ivar Ingimarsson in the right corner and crossed for Danns to crash home.
But Reading were handed a lifeline on the half hour when Paddy McCarthy was adjudged to have brought down Long in the area.
The striker picked himself up to thump in the penalty and finally breach fortress Selhurst.
Four minutes later, busy referee Bates pointed to the spot at the other end after Royals keeper McCarthy tripped Iversen.
Ambrose stepped up to take the penalty but McCarthy guessed correctly, diving to his left to make a fine save.
Five minutes into the second half, Reading were back on level terms after Long turned provider to set up Kebe, who lashed his first-time shot past Speroni.
But Eagles boss Dougie Freedman threw on Easter and the move paid immediate dividends, the striker chipping up Dean Moxey's cut back before turning and hitting an unstoppable volley past McCarthy and into the net.
However, with 17 minutes remaining Hunt met Jobi McAnuff's cross with a far-post header to ensure the visitors pocketed a point.