Warren Gatland admitted Wales sent on the wrong player from the bench during a sobering 24-19 defeat to Fiji, on another dark day for Welsh rugby.
Fiji triumphed for the first time in Cardiff as Wales suffered a record-equalling 10th Test consecutive defeat.
If that unwanted piece of history was not bad enough, the post-match inquest revealed an element of farce as head coach Gatland said Wales had incorrectly replaced injured winger Mason Grady in the 17th minute with outside-half Sam Costelow.
Wales had gambled on a 6-2 split on their bench with only two backs available and assistant coach Rob Howley stressed at the pre-match captain's run that scrum-half Ellis Bevan would replace an injured winger.
But Costelow played on the wing until the 64th minute before replacing Gareth Anscombe at outside-half. Bevan came on to the wing at that point and scored Wales' third try in the closing stages.
"Ellis was supposed to go on," Gatland confirmed after Fiji overcame Wales for only the second time in the history of the fixture.
"I need to get to the bottom of that. We were talking and said we're going to put Ellis on and then Sam's ran on the field.
"I think he might have assumed he was the person going on.
"We had already had those discussions with Ellis that if we do lose a winger, you're going to need to cover us there."
Wales' latest defeat matched a run of losses set in 2002 and 2003 under Gatland's fellow New Zealander Steve Hansen.
They have not tasted success since beating 2023 World Cup pool stage opponents Georgia.
Wales led 14-3 but a red card for Semi Radradra - who was sent off for a dangerous tackle midway through the first half but allowed to be replaced due to World Rugby's 20-minute red-card trial - galvanised Fiji.
Fly-half Caleb Muntz scored 19 points through a try, four penalties and conversion, with centre Josua Tuisova's late score sealing matters.
Gatland said: "I'm in favour of it (red card trial) if it's not deemed to be reckless or deliberate.
"There's no arms in there and he's gone for the shoulders, and there's head to head contact.
"If you catch someone high it can be a 20-minute red card, but they've to deem whether it's foul play of a certain standard.
"I think it keeps the game alive and it's probably given Fiji an opportunity to get back in the game. I don't see that as bad for the game."
On pressure building on him during Wales' losing run, Gatland said: "The pressure comes externally, basically from the media as it's a narrative that you create.
"That's OK from where I sit. We've said for the last 12 months since the World Cup, with the number of players and experience that we've lost, that we were going to invest in a group of youngsters we felt we could build with and take us on.
"We've seen development from those youngsters. We've said we need some patience and time. But I understand Test match rugby is about performing and winning."
