Wales coach Warren Gatland could opt to rest Williams, his country's record international try scorer, with an eye on Tests later in November against Argentina and Australia.
But the Lions and Ospreys wing, who stands 5ft 7in, knows that Samoa are never an easy touch.
The Polynesians have won three out of their six encounters against Wales, including humbling losses in the 1991 and 1999 World Cup pool stages on home turf in Cardiff.
"It's not going to be easy on Friday, certainly. We're on about the physicality in defence but, God, they've got some good attacking players as well," Williams added.
"So it makes for a great game, we know it's going to be tough and we're going to have to be on top of our game and we'll look forward to it.
"Of course we need to win, we need to win our next three games and we're more than capable of doing it."
Wales ran New Zealand close on Saturday but still could not find the precious win that has eluded them since 1953.
"We need to pick ourselves up, obviously we're very disappointed. It's not often you... just lose to the All Blacks, feeling like you could have got something out of the game," Williams said.
"We're in a good position at the moment but we can't get complacent... we need to play well on Friday to beat a very good Samoa side.
*Follow the Wales team announcement on all BBC Sport Wales outlets on Tuesday 10 November, 1330 GMT
Backs: Dan Biggar, James Hook, Shane Williams (all Ospreys); Gareth Cooper, Jamie Roberts, Tom Shanklin, Tom James, Leigh Halfpenny (all Blues); Martin Roberts, Stephen Jones, Jonathan Davies, Morgan Stoddart (all Scarlets); Dwayne Peel (Sale/ENG).
Forwards: Paul James, Duncan Jones, Craig Mitchell, Huw Bennett, Alun Wyn Jones, Ryan Jones (capt), Jonathan Thomas (all Ospreys); Gethin Jenkins, Bradley Davies, Andy Powell, Sam Warburton, Martyn Williams (all Blues); Matthew Rees (Scarlets); Luke Charteris, Dan Lydiate (both Dragons).
Backs: Junior Poluleuligaga (Bay of Plenty/NZ), Uale Mai (Apia West), Fa'atonu Fili (Wellington/NZ), Lolo Lui (Apia), Seilala Mapusua (London Irish/ENG), Eliota Fuimaono Sapolu (Gloucester/ENG), Gavin Williams (Clermont Auvergne/FRA), Anitelea Tuilagi (Sale/ENG), Henry Fa'afili (Leeds Carnegie/ENG), Sailosi Tagicakibau (London Irish/ENG), David Lemi (Wasps/ENG), Titi Esau (Apia West).
Forwards: Census Johnston (Toulouse/FRA), Justin Va'a (Glasgow/SCO), Jeremiah Fatialofa (Counties Manukau/NZ), Sakaria Taulafo (Tasman Makos/NZ), Mahonri Schwalger (Sale/ENG), Andrew Williams (Apia West), Filipo Levi (Newcastle/ENG), Iosefa Tekori (Castres/FRA), Kane Thompson (Dax/FRA), Jonathon Fa'amatuainu (Bath/ENG), Ofisa Treviranus (Apia West), George Stowers (London Irish/ENG), Misioka Timoteo (Apia), Henry Tuilagi (Perpignan/FRA), Semiperive Semeane (Apia).
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