After two seasons of defying the odds to keep amung the big boys of the First Division Grimsby must surely face relegation this time.
They slumped to the bottom of the table with Sheffield Wednesday's shock win at Portsmouth and next up for the Mariners is a visit to Hillsborough.
There were no such worries for Palace who made the most of some shocking defending to stroll to a comfortable away win.
They managed four goals in the end but they could have doubled their tally with 2nd half substitute Dougie Freedman spurning the chances of a hat-trick.
The sub finally added an excellent goal in the final minute after Grimsby had briefly raised hopes with a 47th minute header from central defender Steve Chettle.
But by the time they scored the Mariners were three goals adrift after some shocking defending.
A sickness bug affected the Grimsby line-up, but that was no excuse for some shocking defending that led to Palace's first-half goals.
Youngster Wayne Routledge went through for the first on 17 minutes and then two goals in a minute on 33 and 34 minutes from Noel Whelan and Julian Gray killed off Grimsby's hopes.
The Mariners were booed off by their home fans at half time and although their was an improvement at the start of the second, Palace quickly regained control as they avenged last season 5-2 defeat on the same ground in some style.
For Grimsby the end of the season cannot come quick enough and although they could still escape as they have to play Brighton and Walsall as well as Wednesday, the task looks beyond them.
Palace who made five changes from the midweek home defeat by Watford can start planning for next season and with the youngsters having come to their side from the youth team, the future at Selhurst Park looks considerably brighter.