Pritchard and Roberts did not play in last Saturday's 14-14 draw against Scotland, which earned Samoa a play-off berth due to a superior for-and-against than the Bravehearts.
Papua New Guinea coach Michael Marum has also named star five-eighth Ase Boas for Sunday's quarter-final showdown with England in Melbourne after resting the Queensland Cup player of the year from last weekend's 64-0 defeat of USA.
Lachlan Lam makes way for Boas, despite scoring two tries in his Test debut for the Kumuls.
