The Samoans, a Tier Two rugby nation, have an impressive record against Wales at the World Cup, winning both their encounters in 1991 and 1999.
Samoa vice captain Seilala Mapusua, however, said there was no doubt which team were tipped to win.
"Wales are the favourites, make no bones about it," he said. "They are ranked ahead of us in the IRB rankings. Hopefully the pressure is on them. We are one of the minnows and we hope to upset them.
"We've put a bit of pressure on ourselves as well. We've got no excuses. It's good to have pressure."
World champions South Africa, currently ranked 3rd in the world, head up the group, with Wales (6th), Samoa (10th), Fiji (15th) and Namibia (20th) also battling for one of the two qualifying spots.
Wales lost 17-16 loss to South Africa in their opener last Sunday while Samoa hammered Namibia on Wednesday.
Mapusua conceded it would have been nice to have had a full week to recover like the Welsh did.
"It's tough to play test matches with a four-day turnaround. But it's the cards we've been dealt and we knew that from the start. We've just go to get on with it," he added.
Wales assistant coach Rob Howley said improved mental toughness and some good results against Six Nations teams had helped set new standards and expectations within the team and they were looking forward to the Samoan challenge.
"There's always been a question on mental toughness. I think the words composure and confidence come to mind," he added.
"We've got high standards. We showed those high standards last Sunday and it's important we get to those high standards tomorrow afternoon."