Argentina's youngest side at a World Cup since 1999 will face an experienced Tonga side with a total of 349 caps and the oldest average age in the tournament at 31 years and 38 days.
The Pumas have made seven changes from the 54-9 win over in Gloucester last week which followed their opening 26-16 loss to world champions New Zealand.
"Against Georgia we had problems in the first half. We weren't good in ball winning, lineout and scrum which are areas where we draw our strength," Sanchez said earlier this week of the first half against Georgia after which they led 14-9.
"The idea is to play at the same level for 80 minutes. If we start the same way with Tonga as we did against Georgia, they’ll grow stronger because they have better individuals.
"We must try to beat them as a team. If you close them down and put them under pressure in the forwards you can beat them, but if you get drawn into their disorder things get complicated."
The Pumas are well aware that Tonga, upset 17-10 in their opening match by Georgia before beating Namibia 53-21 this week, are capable of shocking any team on their day, as they did when they beat France in a pool match four years ago.
Tonga coach Mana Otai, whose side are a point ahead of Argentina in the pool standings with one win and two bonuses, concurred with Sanchez about the strength of the Pumas.
Conceding the Argentine's superiority in the set piece, Otai said his team would need to spring a surprise or two at the Leicester City Stadium (kickoff 1330 GMT).
"It's always about the element of surprise. Games now are analysed fairly heavily and it's a mental game as well. You have got to keep the opposition guessing all the time," Otai said.
"If you keep running your head into a brick wall, you have got to find the door. Sometimes it helps if you can’t find the door, then you create one.
"This game is going to be a defining moment for us and we are approaching it that way."
Teams:
Argentina: 1-Marcos Ayerza, 2-Agustin Creevy (captain), 3-Ramiro Herrera, 4-Guido Petti, 5-Tomas Lavanini, 6-Pablo Matera, 7-Juan Martin Fernandez Lobbe, 8-Leonardo Senatore; 9-Martin Landajo, 10-Nicolas Sanchez, 11-Juan Imhoff, 12-Jeronimo de la Fuente, 13-Matias Moroni, 14-Santiago Cordero, 15-Joaquin Tuculet
Replacements: 16-Julian Montoya, 17-Lucas Noguera, 18-Juan Pablo Orlandi, 19-Matias Alemanno, 20-Juan Manuel Leguizamon, 21-Tomas Cubelli, 22-Santiago Gonzalez Iglesias, 23-Horacio Agulla
Tonga: 1-Soane Tonga'uiha, 2-Elvis Taione, 3-Halani Aulika, 4-Tukulua Lokotui, 5-Joseph Tuineau, 6-Sione Kalamafoni, 7- Nili Latu (captain), 8-Viliami Ma'afu; 9-Sonatane Takulua, 10-Kurt Morath, 11-Fetu'u Vainikolo, 12-Sione Piukala, 13-Siale Piutau, 14-Telusa Veainu, 15-Vungakoto Lilo
Replacements: 16-Aleki Lutui, 17-Sona Taumalolo, 18-Sila Puafisi, 19-Sitiveni Mafi, 20-Opeti Fonua, 21-Samisoni Fisilau, 22-Latiume Fosita, 23-David Halaifonua
Referee: Jaco Peyper (South Africa)
(Editing by Nick Mulvenney)
