New Zealand coach Graham Henry gave his side "six or seven out of 10" after the hosts beat Tonga 41-10 in the opening match of the 2011 World Cup.
The All Blacks, bidding for their first title since winning the inaugural tournament in 1987, ran in six tries but fell away after a fine first half.
"It's early in the tournament, there's a bit of tension," added Henry.
"We scored some good tries, defended well, made too many mistakes - there's a bit of work to be done."
Henry recalled that in 2007 his side opened with a comprehensive victory but went on to lose in the quarter-finals to France.
"I revert back to the last World Cup in 07. The easy win against Italy didn't do us much good," said Henry.
There were positives for the All Blacks, who looked impressive in the first half as they ran in four tries to race into a 29-0 lead in Auckland.
Centre Sonny Bill Williams and full-back Israel Dagg, who scored two tries, both shone and Henry had words of praise for the two players.
The coach added: "We scored some good tries and got maximum points, competed well and had a good structure."
All Blacks captain Richie McCaw was far from happy with the way his team's performance fell away after the break.
"If you are up by some points, the good teams are the ones that keep their pressure on regardless of what the scoreboard says and that is something we will have to address a bit," said McCaw.
"We need to look at the reasons why we made mistakes. Was it because we were a little bit over eager, or whether or not we were trying too much? I'm not too sure.
"For the most part I think we did some good stuff early and we just have to make sure we do that for the full 80 minutes."
Tonga coach Isitolo Maka said some of his players had been "overwhelmed" by the occasion.
"Some of the players looked really nervous," he said.
"But to score 10 points against the All Blacks, I'm very, very proud."