Manu Samoa won the first leg 42-13 in Auckland last weekend, with the aggregate winner from the two games sealing their spot in France in 2023.
Tonga only trailed by three points at half-time and prop Ben Tameifuna said they need to sustain their performance over 80 minutes.
"There was some bloody good things that happened last week and it was just towards the end there the boys folded a little bit but this week's just being able to do what we did but for much longer."
James Faiva is back at first five, having recovered from an ankle injury suffered against the All Blacks two weeks ago.
With rain forecast throughout the match, he believed it was crucial Tonga's kicking game and on field management is up to scratch.
"What I can offer the boys, driving the boys and saving their energy in some part of the field," he said.
"Last week I think we tend to play a bit more rugby in our own half, rather than kicking the ball and trying to save our energy and just try to play a territory game."
There's no denying Samoa is in the box seat, with Samoa coach Vaovasamanaia Seilala Mapusua adamant they will playing to win on the night and not just protect their 29 point buffer from the first leg.
The Manu announced a late change on Saturday morning, with debutant hooker JP Sauni coming onto the bench after Seilala Lam picked up an injury during Friday's captain run.
The losing team will have to back up against the Cook Islands next weekend and Tonga captain Sonatane Takulua said they will give it their best shot.
"29 points we have to beat but we've just got to come up and put everything we've got into the game and we come out the end with it," he said.
"We've just got to take every point we can and get a lot of points."