That means the Pumas realistically require a bonus-point win over the Pacific islanders this weekend if they are to deprive France of the second qualifying spot.
"What pains us is how well we played in one half and how badly in the other, knowing all the time that we are perfectly capable of playing 80 minutes of high-intensity, intelligent and fast rugby," said Pumas centre Jerónimo de la Fuente.
"We are fully aware of how important the clash with France was, and it hurt to lose. We are fully confident that we will show up against Tonga, and against England and the USA afterwards."
Meanwhile, Argentina coach Mario Ledesma insisted all was not lost for his side.
"We must do what we set out to do," Ledesma said. "Against France, we didn't in the first 40 minutes, so this time we must remain focused and overcome our mistakes. The most dangerous teams are the ones who aren't afraid to make mistakes."
Pumas captain Pablo Matera added: "If we are talking about confidence, the team stands firm and tall, because what we did during the second half with France we can always replicate."
Tonga were well beaten 35-3 by England in their opening match of this World Cup, with the defeat made worse by the fact both centre Nafi Tuitavake (arm) and fly-half Kurt Morath (throat) suffered tournament-ending injuries.
Their last World Cup match against Argentina, a 45-16 loss in England four years ago, literally left its mark on some Tonga players.
"The physicality was much improved from the previous game (a 92-7 warm-up loss to world champions New Zealand in Hamilton)."
As for facing the Pumas, the centre added: "It will be another physical battle come Saturday. The scrum and line-out is also our strength and if we can match them I think we will have a good platform."
And turning to Uruguay's 30-27 defeat of Fiji, Piutau said: "We have seen there is a chance there. Once the stars are aligned there's a wonderful opportunity for us."
Ledesma sent a message to his Argentina squad by dropping arguably the most influential player and the former captain for Saturday's must-win game.
Furthermore, the coach benched fly-half Nicolás Sanchez and hooker Agustín Creevy without any ego-soothing explanations as to why. Because in the days since last weekend's dramatic 23-21 loss to France, his approach has been all about re-building the squad dynamic rather than pandering to the wounded pride of big-name players.
"The message hasn't changed, not just from this staff, but from any the Pumas have ever had. The key thing in wearing the Pumas' shirt is to do your best," Ledesma said. "Nobody can take it for granted. Everyone who's worn this shirt knows it. That's the name of the game."
Ledesma, a hooker who played 84 times for Argentina, usually talks to players who have been left out and explains to them why. But he felt he needed a change, perhaps sensing something had been lacking in the game against France.
"I believe this week we had to think collectively, as a group," he said. "Until last week we always took the time to talk with those not selected, but this week was different."
Creevy has 12 appearances at the World Cup, while Sánchez has notched a career 102 World Cup points. But neither player is bigger than the Argentine cause — which is to win the next three Pool C games against Tonga, 2003 champion England, and the United States.
Expect Ledesma's players to come out firing early on with some aggressive front-foot rugby at Hanazono Rugby stadium, on the outskirts of Osaka. It would be the best way for the Pumas to banish the memory of a dismal first-half performance against France, which led 20-3 at the break last Saturday.
"Our mindset [is] very ambitious, perhaps, but we must do what we set out to do," Ledesma said. "Against France, we didn't in the first 40 minutes, so this time we must remain focused and overcome our mistakes. The most dangerous teams are the ones who aren't afraid to make mistakes."