The visitors were in front inside 10 minutes as Robert Huth rose highest to nod past Wayne Hennessey, and Jamie Vardy doubled the advantage on the counter just after half-time.
But Palace wrestled back to grab a point as first Yohan Cabaye rolled an effort past Kasper Schmeichel before Christian Benteke sealed a precious draw.
The Foxes named a strong starting XI despite having one eye on Tuesday's Champions League quarter-final against Atletico Madrid.
And the travelling Leicester fans were celebrating early as Huth abandoned marker Luka Milivojevic to dampen any positivity which remained at Selhurst Park following Monday's 3-0 win over Arsenal.
Benteke, Jason Puncheon and Wilfried Zaha all went close as Palace knocked on the door before the break, but referee Mike Dean's whistle ended a frustrating first period for the Eagles.
The hosts were stung on the break shortly after half-time as Jamie Vardy appeared to put the game beyond Palace and leave Sam Allardyce looking fearfully over his shoulder in the relegation scrap.
But the Eagles responded instantly and their was an immediate shift in momentum.
Jeffrey Schlupp, playing against his former club, found space on the left and was fortunate to see his pulled effort fall into Yohan Cabaye's path on the penalty spot with the Frenchman supplying the finish.
Zaha then jinked into space on the left and fired over, before a desperate block from Huth kept the Ivory Coast international's low cross away from danger.
Vardy gave Palace a reminder of Leicester's potence on the break, but Schlupp marshalled the England striker out and the hosts made their pressure count with 20 minutes remaining.
Benteke got the better of Yohan Benalouane at the back post to divert Andros Townsend's cross into the ground and past Schmeichel.