In contrast Ireland steamrollered Romania 82-8 to take command of the pool, but with Tonga up next and South Africa and Scotland to follow, things are about to get more difficult for the Irish, especially in the scrum.
"Sometimes in scrummaging, there is no replacement of displacement, weight makes it heavy, it makes it hard because of the nature of it," Ireland prop Tadhg Furlong told reporters on Friday.
"It's a big challenge, it's a big pack and we have to be technically good."
Fullback Hugo Keenan picked out his opposite number Charles Piutau as one to watch when the Tongans start their campaign.
"He is a serious player, isn't he? He is a real danger threat for them and has shown it for years now, he is experienced," Keenan said of the New Zealand-born Piutau.
"They have threats across their backline and in the pack, so we've got to familiarise ourselves with them, but we've known some of their threats for years."
Tonga assistant coach Tyler Bleyendaal said his side were under no illusions about the strength of competition they would face in the pool.
"I think the reality is they are much better, more complete teams than us because they compete at a much higher level of competition more often," he told reporters.
"But that doesn't change our ambition, our preparation, to try and knock over all of the teams in our pool ... we're not delusional to the challenge we face, but we are excited."
