Samoa need to win the clash to give themselves a Pool D advantage over the Pumas, who lost their first game to England a fortnight ago.
England have two wins from two games and are top of the points table in the pool.
Samoa are second but need the win to give them a better chance of qualifying for the quarter-finals.
Mapusua said they are focused on stopping the South Americans, but they will need to execute correctly.
“We are going to have to stop Argentina from doing what they do by doing what we do and committing to how we want to play,” he told the media at the team naming in Saint-Étienne on Wednesday evening (French time).
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“We are under no illusion to the threat Argentina pose and we believe that if we stick to how we want to play and play the Samoa way, I am confident we will be able to stop Argentina.”
He said the three players who have been given starting roles are being brought in against the Pumas because of their strengths.
“Brian [Alainu’u’ese, second row] has been training really well and this was a game we thought his strengths would be utilised, especially around the set-piece,” he said.
“Ben Lam has just become available after sustaining an injury a few weeks ago. He is now fit and ready to go.
“We were worried when he sustained his injury. He’s a lot on the edge for us, he’s a very big man who can move quickly ... he brings a lot to the wider channels, his pure power and the way he plays the game. We are looking forward to finally getting him on the field this weekend.”
Sopoaga ruled out
But he will not have former All Black Lima Sopoaga, who came off the bench against Chile last weekend.
“With Lima Sopoaga’s omission [from the match-day squad], I think it’s been circulated, he sustained a [calf] injury last week against Chile,” the coach revealed.
“He was ruled out this week, we ruled him out as a precautionary. Also, because of the nature of his injury, he wasn’t ready to play this week. We will reassess at the weekend towards next week’s game.”
Mapusua said his team understood how important it was for them to start well, remain consistent and finish strong, unlike their first-half performance against Chile.
“The boys have realised we are in the tournament, we’ve arrived at the party. There are no second chances so this week the whole squad, there has been a real lift and energy. We know we have got a huge game coming up,” he said.
“We won’t be short of motivation.”
‘Confidence in what we are doing’
Fiji’s win over Australia last weekend is motivation also for the side as they go into the battle with what Vaovasamanaia calls an “injured Los Pumas”.
“We had confidence before the game, confidence that Fiji were going to get over and also confidence in what we are doing. That’s awesome to see our Pacific brothers doing really well and we are always going to be behind them until we have to play each other.
“We are proud of them and of course we are going to take inspiration and confidence from that. But I’d be more inclined to take confidence from the work and preparation this group of men have done over the past few months.”
Flyhalf Christian Leali’ifano will man the pivotal playmaker role and said he is excited to meet Argentina, coached by his former Wallaby headman Michael Cheika.
Cheika was Wallabies coach at the 2019 Rugby World Cup where Leali’ifano was a key player for the side.
“Excited for the challenge ahead,” Leali’ifano said.
“Not only a former coach there in Michael Cheika but just the challenge that lays ahead for this team, this group to play a tier-one nation that historically did really well at a World Cup.”
The Samoa vs Argentina clash kicks off at the Stade Geoffroy-Guichard, Saint-Étienne at 3.45am (NZ Time) or 4.45am in Samoa on Saturday.
Samoa team: 1. James Lay, 2 Seilala Lam, 3 Paul Alo-Emile, 4 Brian Alainu’u’ese,5 Chris Vui (c), 6 Theo McFarland, 7 Fritz Lee, 8 Steven Luatua, 9 Jonathan Taumateine, 10 Christian Leali’ifano, 11 Ben Lam, 12 Tumua Manu, 13 Ulupano Junior Seuteni, 14 Nigel Ah-Wong, 15 Duncan Paia’aua; Reserves - 16 Sama Malolo, 17 Charlie Faumuina, 18 Michael Alaalatoa, 19 Taleni Junior Agaese Seu, 20 Sa Jordan Taufua, 21 Melani Matavao, 22 Alai D’Angelo Leuila, 23 Danny Toala
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