Skipper Bryan Redpath admitted mis-firing Scotland were flattered by the 32-11 win over Japan after his team struggled to subdue the battling underdogs in Townsville.
The experienced scrum-half operated behind a pack which dominated early on but failed to control the match as Japan defended tenaciously and forced the Scots into several errors.
The Scots made far too many elementary handling mistakes and were ragged from set plays, losing possession from three second half line-outs.
Another area for concern was the poor kicking of Chris Paterson, who scored 15 points with two tries, a penalty and a conversion, but missed four other straightforward attempts with the boot.
Scotland appeared to avoid any injuries but will have to pick up a gear or two if they are trouble fellow Pool B opponents USA, France and Fiji.
"We were definitely a little bit shaky, a lot of passes went down," said Redpath.
"There was a lot of lost ball on contact, which just showed that we had not played in five or six weeks.
"There is a lot of work for us to do in the eight days before we play the USA."
Redpath paid tribute to the Japanese, who constantly troubled Scotland with disciplined defence and were unlucky not to add to their one excellent try with some speedy play on the break.
"They were very competitive," he added. "But our game was not up to standard and we are very disappointed with that. Credit to them but disappointment for us."
But Redpath was pleased to have come away from such a work-out with the win and a bonus point from the five-try display.
"We started brightly and finished brightly but that doesn't win you games when they get a bit tougher.
"Full credit to Japan, they tackled really well. They made us work hard and we panicked sometimes."
Scotland coach Ian McGeechan conceded his team's rearguard had been stretched and exposed at times.
"It was poor defence," he answered simply when asked what had been at the heart of the unconvincing display.
"We picked up the wrong runners and the ball was coming back too quickly," he said.
"But having said that, I thought the scrambling defence worked very well."