That killed the contest off once and for all. Jefferson Lerma saw one fierce strike from distance go over.
Matheus França came off the bench for Palace to make his first Selhurst appearance since February of last year; the Brazilian, in the closing stages, narrowly fired wide.
The game was won, however, and Palace were able to celebrate reaching the FA Cup quarter-finals for the third time in seven seasons with a sweet victory over their local rivals.
Palace: Turner (GK), Richards, Lacroix, Guéhi, Muñoz (Clyne, 89), Hughes (Wharton, 65), Lerma (Devenny, 89), Chilwell, Eze (França, 85), Sarr (Esse, 65), Mateta (Nketiah, 15).
Subs: Henderson (GK), Mitchell, Kamada.
Millwall: Roberts (GK), Cooper, Tanganga, Mitchell (Honeyman, 66), Azeez, Bryan, Coburn (Ivanovic, 66), (De Norre Saville, 66), Cundle (Jensen, 12), Harding (Emakhu, 85) Neghli (Bangura-Williams, 32).
Subs: Wallace, Wintle, Sturge.
As It Happened