Eddie Jones said Japan were "going in the right direction" despite being thrashed 52-17 by England in Tokyo on Saturday in the first game of his second stint in charge.
An inexperienced Japan side featuring four debutants in the starting lineup and four coming off the bench conceded eight tries but scored two of their own in a stirring finish to the game.
Jones, who took England to the World Cup final in 2019, said he saw promising signs as he tries to instil a high-tempo playing style in his new team.
"We showed enough in attack to know we're going in the right direction but we were unable to capitalise," said the Australian.
"We've got eight new caps today that have all had a fantastic learning experience, and sometimes you get a lesson before you get anything else, and they got that today."
Japan opened the scoring with a penalty in sweltering conditions in the Japanese capital before pinning England back on their own goal-line for most of the opening 10 minutes.
England weathered the storm and scored four tries in the first half, with fly-half Marcus Smith influential.
Jones said his team would have to "build up the physical and mental capacity" to deliver for the full 80 minutes.
"The first 15 minutes of the game, we had England under pressure – we took the game to England," he said.
"It's just practice. Hard practice. We'll get there."
Jones's time in charge of England ended on a sour note when he was fired at the end of 2022 after a run of poor results.
The feisty 64-year-old said he enjoyed being reunited with his former team.
"I think when you play against a team you've coached, it's always a bit of fun," he said.
"It makes it a bit more interesting. You know the players.
"Some of the young players you bring through and you want them to do well, you just don't want them to do too well against you."