The scene was set for Palace, the penniless team Warnock quit last month for the riches of west London, to leapfrog Rangers in the table with a victory.
Instead, Warnock twisted the knife as Akos Buzsaky's early strike and Kaspars Gorkss' second-half header brought Palace's recent revival shuddering to a halt.
The Eagles, who are still in administration, are now just a place and a point above the drop zone while Rangers can breathe easier after a first win in eight.
Warnock, who claimed prior to the match that he was in a no-win situation as he does not want to see Palace relegated, received a mixed reception before kick-off.
He had barely reached the dug-out when, five seconds in, Rangers centre-half Damion Stewart was involved in a sickening clash of heads with Eagles striker Calvin Andrew.
Stewart had to be stretchered off while Andrew soldiered on before eventually having to be replaced.
By then, Rangers had already taken an 11th-minute lead after Palace failed to clear Hogan Ephraim's cross and Buzsaky rifled his 11th goal of the season from the edge of the area.
Buzsaky, who has been in and out of the team since Warnock took over, looked eager to make the most of his latest chance and nearly doubled the lead with a dipping volley which flew just over.
Palace would have equalised eight minutes before the break but for a stunning save from Rangers keeper Radek Cerny. Overlapping left-back Clint Hill looked certain to score after being put through by Darren Ambrose but Cerny kept out his shot at full stretch.
Rangers could have gone further ahead shortly after the break when Ephraim chested Adel Taarabt's pass into the path of Tamas Priskin but the Hungarian striker's shot was wayward.
But they did double their lead on the hour when Taarabt swung in a corner and Gorkss got ahead of his marker to head home.
Palace, to their credit, did not give up and Stern John volleyed over before Neil Danns squandered two decent chances, rolling a shot wide before firing another straight at Cerny.
But Warnock was able to enjoy a happy return to his old manor while Palace's season looks set to go to the wire.