Rhodes was presented with Rovers' player of the season award before kick-off and scored his 27th goal since joining from Huddersfield in August.
Barnsley and Rhodes' former club are two of the four teams that lie between Blackburn and the drop zone and the fact that the Yorkshire rivals meet each other to round off their seasons means Ewood Park caretaker boss Gary Bowyer can breathe easily.
Palace led through Stephen Dobbie but Ian Holloway's men may look uncomfortably over their shoulders from fifth position next weekend if they do not secure their play-off spot with a win at Millwall on Tuesday night.
Opportunities were few and far between until midway through the half when Blackburn established themselves as an attacking threat - Joshua King's cutback narrowly evaded Nuno Gomes after a driving run and, moments later, Rhodes fired over on the turn.
Back came Palace and Blackburn defended a flurry of corners successfully only to see their good work undone in the 28th minute.
Dobbie collected Aaron Wilbraham's flick-on and got the better of Grant Hanley to produce a smart finish.
King released Rhodes following a fine pass from Josh Morris and the Scotland international burst clear to deftly lift the ball over Julian Speroni and home from an acute angle.
Five minutes into the second half Morris was involved once more, twisting and turning before going down under a challenge from Kagisho Dikgacoi. Referee Phil Gibbs was unmoved.
The young full-back could not stay out of the action and soon afterwards Rhodes and David Goodwillie came close from his dangerous ball into the box.
It was a thrilling end-to-end period and, in the 52nd minute, Glenn Murray rattled the crossbar after a long ball undid the Rovers defence.
Rhodes was alert when Palace coughed up possession with a quarter of an hour remaining but strike partner Goodwillie thrashed over left footed when played in.
The final chance fell to Damien Delaney who headed wastefully wide from close range after Dikgacoi picked him out.