The pair was given an emotional haka as a send-off from their teammates with the victorious French players also linking arms and watching on to show their respect.
"Rugby has been a big part of my life and it still will be but I just won't be taking the field alongside the girls," said Fa'amausili.
"I've played my part in helping, progressing and nurturing players and so now I need some 'me time'.
"It was very, very emotional. Just looking at the girls doing the haka at the same time with tears is pretty emotional but I am so proud of them. We are one big family and when one person cries everyone cries."
The Black Ferns found themselves on the back-foot from the kick-off, with tight-head prop Julie Duval's try giving France the early lead before New Zealand centre Stacey Waaka wrestled over to help level the scores at 7-7 after 14 minutes.
France then took control with centre Maelle Filopon and No 8 Romane Menager stunning the Black Ferns with two long-range tries before Fa'amausili crossed to keep the visitor's hopes alive.
Drouin ran in another brilliant try to extend the home side's lead to 10 early in the second-half, before the Black Ferns hit back in the 48th minute with a five-pointer to fullback Selica Winiata.
Itunu tried everything she could to lift her teammates after being promoted to the starting line-up at No 8 in place of Les Elder, but limped off with five minutes remaining before the French celebrated a historic win.
France 30 (Julie Duval, Maelle Filopon, Romane Menager, Caroline Drouin tries, Drouin 2 cons, 2 pens)
Black Ferns 27 (Stacey Waaka, Fiao'o Fa'amausili, Selica Winiata tries, Kendra Cocksedge 3 cons, 2 pens)
HT: 19-14 France