Wales wilted in the Kitakyushu heat to lose 24-19 to Japan and suffer an 18th successive Test defeat.
First-half tries from Ben Thomas and Tom Rogers, as well as a penalty try and a Sam Costelow conversion, gave Wales a 19-7 interval lead and hopes of a first victory since beating Georgia at the 2023 World Cup 21 months ago.
But Japan dominated the second half and tries from Takuro Matsunaga, Ichigo Nakakusu and Halatoa Vailea, plus nine points from the boot of Seungsin Lee, piled on more misery for Wales.
Brave Blossoms boss Eddie Jones said he had hoped for a hot day to “run Wales off their feet” and the oppressive conditions – with the temperature above 30 degrees Celsius as well as high humidity – meant water breaks in each half and an extended interval.
A slippery ball produced countless handling errors and there was often little rhythm to a disrupted contest that took over two hours to complete.
Taulupe Faletau, Nicky Smith, Ben Thomas and Blair Murray survived from the 68-14 thrashing to England in the Six Nations as interim head coach Matt Sherratt made 11 changes.
Number eight Faletau – the fifth-most capped Welshman – made his 109th appearance but it was largely an inexperienced line-up with six starters having fewer than 10 caps.
Wales’ fall from grace had left them in 12th place on World Rugby’s rankings table, one spot above Japan, and it was very much a meeting between two teams in transition.
There was a worrying start to the contest as Ben Carter took a hit to the side of the head inside 30 seconds.
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Carter slumped to the ground after attempting to make a tackle and there was a lengthy stoppage before the second row forward was taken away on a stretcher.
Wales immediately shrugged off that blow as Faletau exploited space profited from a line-out ploy to send Thomas over with a well-timed pass and Costelow converted.
Japan were on the backfoot and struggling to get out of their own half, but scored from their first attack after 16 minutes as winger Kippei Ishida sliced through midfield to set up Matsunaga and Lee’s kick restored parity.
Wales hit the front again with a penalty try after Nakakusu, who had replaced the injured Matsunaga moments earlier, deliberately slapped the ball away as Josh Adams closed on Kieran Hardy’s chip by the try line.
Nakakusu suffered further punishment with a yellow card, and Wales took advantage of their extra man after Japan had found touch from the kick-off.
Faletau broke away from a scrum going backwards and Hardy, Costelow and Johnny Williams moved the ball on for Rogers to scamper into the corner.
The tide turned in the second half as Amato Fakatava saw his effort ruled out for a Shinobu Fujiwara knock-on, but Japan were not to be denied after going through the phases.
Rogers slipped off a tackle and Nakakusu dived over with Lee adding the extras and soon reducing the deficit to two points with a penalty.
Japan got their noses in front for the first time as replacement Vailea barged over and Lee’s sparked celebrations that continued until the final whistle.
The two-match series will conclude in Kobe next Saturday.
