Scotland boss Vern Cotter admitted that his players had grown more nervous having to wait for their first Rugby World Cup match before defeating Japan.
Cotter's side are one of the last to get going in the tournament and did so in style by running in five tries in the second half in Gloucester.
The former Clermont boss praised Japan's abtilies in attack and was glad to see his side show real mental resolve.
"I wouldn't say it was convincing. We scored points in the second half, I thought we traded blows in the first half and we were unlucky to not score before half-time," Cotter said.
"Hats off to Japan. They're very difficult to play against, deft passers of the ball and they change their angles well in attack.
"We've very happy to get the win and happy to pull away in the second half and get started. Happy to get started too. Watching everyone play has been a bit nerve-wracking for our players. We did well to keep our composure during difficult moments."
Cotter added that little had changed in terms of Scotland's prepartions after Japan's shock win over South Africa last weekend.
"We've been watching Japan for two and a half months and we weren't surprised by their tenacity or commitment. They've had this Rugby World Cup firmly in mind for a long time and it showed for a long time today. They were 100 percent committed. It was a great Test for us," he stated.
"[The surprise win] just reinforced a lot of what we thought. Our guys adapted well to their new players that they brought in.
"There was constant pressure. Once we score we'd like to make those scores stick and we'll be looking at how we can stop teams from coming back in."
Scotland have no major fitness concerns, only requiring "a couple of stitches" according to Cotter, but he admitted that his side's own four-day turnaround before facing the USA would be a challenge.
"They found it hard with the turnaround and we're in the same situation now. We'll be focusing on recovery and trying to regenerate energy levels. We've got 31 players ready to put their hands up for the next game and in the next 48 hours we'll have a look at who has bumps and bruises."
Scotland captain Greig Laidlaw, who finished with 18 points on his home club ground, said that Japan's shock win had actually helped to improve his side's performance, adding that he had been able to sense when they were beginning to run out of steam.
"All credit to Japan. I don't think South Africa thought they were would be that physical. We got to watch that and we were a little nervous at the start, and having watched that game we knew there was no place for complacency," Laidlaw revealed.
"I felt they were starting to blow at half-time to be honest and we were starting to hold onto the ball a bit more to put them under pressure.
"The message at half-time was don't panic, to hold the ball and that we had them fitness wise. I believe this Scottish side is one of the fittest for some time and we've seen that in the warm-up games and today."