Tonga were much more competitive after the break and Graham Henry's home side had a poor third quarter by their high standards.
The Tongans got the try their efforts deserved when Alisona Taumalolo scored from close range, but Ma'a Nonu had the final say for the hosts with their sixth and final try pushing the scoreline out to 41-10.
Jonathan Sexton and the rest of the Ireland squad trained early in the morning at New Plymouth Boys High School, before Declan Kidney announced the team and replacements for the USA game at an afternoon press conference.
In between some fiercely competitive games of table tennis at the team hotel, Sexton kept a close eye on the goings-on at Eden Park.
"We all became Tongan supporters in the Ireland team room for the second half of the opening match - well, that's when we weren't captivated by more pressing struggles on the table tennis table," he wrote in his latest O2 Rugby blog.
"The tension in the team room is palpable when the table tennis gets underway. A graphic illustration is that players have been known to go for showers - it's quite warm - after a match such is the intensity of the competition. Brian O'Driscoll and Ronan O'Gara probably head the betting."
There are a number of heavyweight battles in prospect with the management also getting in on the act, although there are murmurs of some underhand tactics at play.
"There is a suspicion that some match fixing will be in the offing after the full first round draw was revealed," joked Sexton.
"I have been pitted against team manager Paul McNaughton and let's just say I respect him as an adversary and expect to lose. I would imagine that Paul O'Connell would have similar misgivings with regard to his first round clash with forwards coach Gert Smal."
Regarding the serious business of getting Ireland's World Cup campaign off to a winning start on Sunday, the Leinster ace readily accepts that the men in green will have to maintain their poise and concentration against a physically pumped-up American side.
"New Zealand started pretty well and looked quite good initially but the manner in which Tonga fought back underlines the importance of maintaining concentration for the entire game.
Ireland will field their youngest half-back pairing for some time when World Cup debutants Sexton (26) and Conor Murray (22) take to the Stadium Taranaki pitch.
The Dubliner rates his new team-mate Murray highly and was on the losing side against him twice last season, as Munster collected the league title.
"Conor's had a great 2011. This time last season he was on a development contract and then got his break," commented Sexton, speaking at today's press conference.
"Everyone's career starts at a certain point. He took his opportunity with Munster and impressed, then took his chance with Ireland and impressed there. He's gone from strength to strength."
Asked what sort of character Murray is, the Heineken Cup winner replied: "He's very laid back and I was shocked that he's so laid back.
"That's a good trait to have and he seems to take everything in his stride. We seem to work well together."
It will be Irish cap number 20 for Sexton this weekend. The August programme of warm-up games did not go Ireland's way results-wise, with successive defeats to Scotland, France (2) and England.
But Sexton, who scored his first international try against the French last month, insists that the squad will be all the better for having played those games when they launch their bid to get out of Pool C.
"There were some disappointing results in the warm-ups. We wanted to win the games, I'm not going to lie about that.
"Maybe at times we played those games like friendlies, viewing them just as warm-up games where results didn't matter.
"But this is the World Cup, this is what we're here for. Maybe we'll look back on those four matches as an important time when we learnt some harsh lessons."
Follow the Ireland team in New Zealand on www.twitter.com/irfurugby.