The Scots, ranked fifth in the world, went down to a disappointing 18-3 defeat against defending champions South Africa in their tournament opener, while Tonga were pummelled 59-16 by Ireland in their first match in a tough Pool B.
Only the pool winners and runners-up advance to the knock-out phase, meaning both Scotland and Tonga must win every match.
"Coming into the tournament we knew that we'd have to perform in every game to have a chance of getting out of this group, which we knew was going to be tough," said Scotland captain Jamie Ritchie.
"We need to be on it for every game."
Tonga, Ritchie added, "have got some extremely good players", notably a handful capped by New Zealand and Australia who have reverted, under World Rugby rules, to play for their country of heritage.
"They are a very physical side and coming into the World Cup they have had an extended period of time together which is something where they usually struggle going into Test matches," he said.
"With that extended period of time together they have got used to how each other plays, they've had time to put in systems. They have some dangerous players out there."
Individual quality
Scotland coach Gregor Townsend said the inclusion of the likes of 17-times capped All Black back Charles Piutau and centre Malakai Fekitoa, who won 24 caps for New Zealand, could only improve the South Sea Islanders.
"They bring their own individual quality but also the experience of playing top-level test matches and at World Cups – and that will spread throughout the team," he said.
"When you've got players like them on the field, they can score a tryout of anything."
With a large contingent of Scottish fans expected at the Stade de Nice, Townsend was focused on one thing only.
"We need to get our World Cup started with our first win. It's our knock-out stage now. If we lose a game, we're out, and we need to go out with that mentality," the former Scotland and British and Irish Lion fly-half.
Tonga coach Toutai Kefu, who was part of the Australia side that won the 1999 World Cup, named an unchanged starting XV from the 59-16 loss to Ireland in their opening game.
The only changes in the match-day 23 come in the shape of lock Adam Coleman, capped 38 times by Australia, and fly-half Patrick Pellegrini coming onto the bench.
"They are our best players and I think after last week's performance, it probably wasn't our best version of us. They deserved another chance," Kefu said of not changing his team.
"The only difference is Adam Coleman comes onto the bench and he might be able to give us a bit of an impact off the bench."
Kefu added: "We are desperate to win. Last week wasn't us, so we want to fix that.
"The dream is to win three games in a row. That would be a dream. We can't look too far ahead of ourselves. We are fully focused on performance."
Tonga scrum-half Augustine Pulu, another with All Blacks experience having won seven caps in the country of his birth, added: "It's knock-out footie this week. We understand what's in front of us and put our best foot forward this week.
"We understand they are quality players but we can only focus on ourselves. Last week we didn't fire our shots so this week we are going to redeem ourselves by going out there and doing our best."
