Following the opening defeat to England, Argentina must beat Scotland at Wellington Regional Stadium in order to progress to the quarter-finals - and Bosch is bullish.
He said: "I think it will be a really tough game, perhaps our most important match in the past four years - we will think of the match as a final.
"We hope to have a good match and we expect to win, of course."
Biarritz back Bosch was a replacement in the 13-9 loss to England, but was thrust into the action midway through the first half following an injury to captain Felipe Contepomi.
He started at centre in the 43-8 win over Romania, a match Contepomi missed due to a rib injury.
Bosch, though, anticipates his skipper will feature against Scotland.
The 27-year-old said: "I expect he will be on the field (on Sunday).
"He is our captain, a very important player for us and I expect the best for him and for us."
Argentina have lost three of the last four meetings with Scotland, including a 2-0 Test series defeat in South America in June 2010.
Asked what he expects from Scotland, Bosch said: "I expect they are going to have a bad day on Sunday.
"Seriously, I think they have a very good team and have progressed a lot in the last few years.
"They keep control of the ball as far as they can. They have a couple of good fly-halves and they are very strong, so I think it's going to be a very tough game.
"The forwards are having a good championship. If they continue in a good way, the backs will follow them.
"We have to continue in our system of playing, our own strategy and I expect to have a good day."
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