Wales interim head coach Matt Sherratt said his team's record losing run had left "scars" after a 24-19 defeat to Japan on Saturday extended it to 18 straight losses.
Wales held a 19-7 halftime lead but wilted after the break in hot and humid Kitakyushu as Eddie Jones's dynamic Japan came from behind to snatch the win in the first of their two tests.
Wales's last victory came against Georgia at the World Cup in October 2023 and their losing streak is a record for a Tier One country in the professional era.
Sherratt refused to blame the 31-degree Celsius heat for the loss and pointed the finger instead at the psychological damage left by his team's dismal form.
"In the second half, some really big moments – I think we had a line-out around 45 minutes to take the game to three scores," he said.
"It was a really tough call from the referee in terms of penalising us.
"When it's a young group and obviously we haven't had a win for a while, those little scars can start to run deep."
Wales lost lock Ben Carter to a head injury in the first minute but tries from Ben Thomas and Tom Rogers and a penalty try sent them into halftime with a comfortable lead.
Japan took control midway through the second half and a try from substitute debutant Halatoa Vailea with nine minutes to go gave them their first win over a Six Nations team since the 2019 World Cup.
Sherratt said Wales would dust themselves down and be ready for next week's second test in Kobe.
"First half, 19-7 lead, so to lose the game at the end is very disappointing," he said.
"It hurts. Already, we've got to use that hurt to fuel next week because the great thing about this tour is that we get a chance next week to put it right."
Japan reached the World Cup quarterfinals on home soil in 2019, beating Ireland and Scotland along the way, but they have struggled for results since Jones returned for a second spell last year.
The Australian was rewarded for naming two uncapped players in his starting line-up and another six on the bench, after debutant substitutes Vailea and Ichigo Nakukusu scored second-half tries to turn the game in Japan's favour.
CARTER RULED OUT
Fly-half Seungsin Lee said Japan's "DNA is to play high-tempo rugby".
"We haven't been able to beat any of the top 10 teams in the world for a few years now so we're happy," said Lee, who kicked a crucial penalty with the tide turning in Japan's favour.
"More than anything, it gives us confidence."
Wales were dealt an immediate blow when Carter went down in the first minute following a heavy head-first collision.
Sherratt said the 24-year-old, who was returning to the team after missing the Six Nations through injury, would not be available for next week's game.
Wales opened the scoring in the fourth minute when Thomas went over after Taulupe Faletau had punched a hole in the Japanese defence from a line-out.
Japan fought their way back into the game and levelled when Takuro Matsunaga finished off a flowing move with a try in the 16th minute.
Nakakusu came off the bench and conceded a penalty try when he swatted the ball away from Josh Adams with the Wales winger in a try-scoring position.
Nakakusu was also sin-binned and Wales took advantage of their temporary numerical advantage when Rogers ran in their third try.
Wales looked in command at the break and captain Dewi Lake said they were "gutted" at how the second half panned out.
"We take nothing away from Japan for the way they played and for coming out on top, but we had moments to win that game and probably put it to bed," said the hooker.
"So it's very, very tough to take."
