England coach Eddie Jones said his team needed a change in attitude to turn around Saturday's test against Japan.
England, completely outplayed for most of the first half, came from 15-10 down at the break to take control and triumph 35-15.
"Maybe we got seduced after scoring an easy try in the first few minutes," he said in reference to Danny Care's third-minute score.
"The players subconsciously think it's going to be easy and that showed in our attitude and effort, which was disappointing.
"Japan are a difficult side to play against if you haven't played them before but I think our second-half response was excellent."
Jones had made 11 changes to the team that went so close to beating New Zealand last week and England certainly looked a different side as Japan ripped through their defence almost at will, scoring through Ryoto Nakamura and inspirational captain Michael Leitch.
They could and should have had more as their quick thinking and sharp handling constantly had England on the back foot and pinned into their own half.
Jones changed things around from the bench in the second half and England soon took total control to come through with 25 unanswered points via tries for Mark Wilson, debutant winger Joe Cokanasiga and Dylan Hartley, backed up by the kicking of George Ford.
"It was a game that tested us today - we put out a different team, different combinations and there wasn't a lot of cohesion. But it was a fantastic test for us and our players will have learned a lot from it," Jones said.
"The attitude was better and we played like England in the second half."
Jones was full of praise for Japan, the team he coached to their famous World Cup win over South Africa in 2015 and who host the tournament next year.
"When I brought them over to Europe we played Georgia, Romania and the French Barbarians," he said. "But now they get to play the All Blacks and England in front of 82,000 at Twickenham. It's fantastic for them. They are a proper rugby country and I'm really pleased for them."
Current Japan coach Jamie Joseph was also happy with the display, though disappointed at the way the team faded.
"We played some really positive rugby and, most of the time, matched the physicality," said the former All Black flanker. "We had some variation which I guess surprised them a bit. "Physically we need to be able to go with the big teams without giving penalties away and our decision-making and accuracy cost us.
"We got a bit sloppy in the second half and allowed them to come back but, in context, to come to Twickenham is a massive challenge for any team and to play the way we did and score the tries we scored... overall we're very happy."