Wayne Pivac criticised Wales' "unacceptable performance" as Italy ended a 36-game Six Nations losing streak by winning 22-21 in Cardiff.
Edoardo Padovani’s last-minute try gave Italy a sensational victory, their first ever on Welsh soil.
But while Italy savoured a first Six Nations success since 2015, the inquest in Wales is likely to be long and hard, with Pivac's side going from champions to also-rans in the space of 12 months.
Wales will finish the 2022 tournament down in fifth place, with their only victory coming against Scotland.
“It’s very disappointing,” said a clearly shocked Pivac. “Lots has happened since last year, that’s been well-documented.
“We came with a goal of giving ourselves an opportunity to finish third, which would have been a superb effort by the boys.
“After round one [when Wales were beaten 29-7 by Ireland in Dublin] we were building each week. But this was an unacceptable performance, which we must not let happen again.
“We had three good performances in this competition and two we weren’t proud of. So it wasn’t the complete competition. We’ll get criticism from it – and rightly so.”
Pivac had made seven changes to the side which had pushed France all the way in Cardiff eight days earlier.
That had led to claims of arrogance and underestimating Italy in some quarters and, on a day when the returning Alun Wyn Jones won his 150th cap and Dan Biggar became the seventh Welshman to win his 100th, Pivac's men floundered in the Principality Stadium.
Tries from Owen Watkin, Dewi Lake and Josh Adams looked to have got Wales over the line as a 21-15 lead was claimed in the final 12 minutes.
But Italy responded in the final seconds as Ange Capuozzo’s burst down the touchline in the final seconds created Padovani’s converted try.
Pivac skirted around Biggar’s post-match assertion in a television interview that this was “probably the last chance for a lot of players”, preferring instead to focus on the summer test awaiting in South Africa and the 2023 World Cup in France 18 months from now.
“Nothing changes in terms of where we are at and what we’re working towards,” Pivac said.
“Obviously that was not part of the plan to lose this game, but we’ll review this game as a coaching group and see why we didn’t have the energy and urgency that the Italians came with.
“If we go to the World Cup and get to the quarter-final, and on to the semi-final, everyone will be very happy.
“We’re not going to lose focus in terms of what the big goal and the big picture is. It’s a bitter pill to swallow for everybody, but we have to learn from this.
“I’m hoping we take a step forward in the summer against the world champions in their backyard, which is going to be a big ask, with an idea of how far we are from them just over 12 months out from the World Cup.”
The only previous time Italy had avoided defeat in Cardiff was an 18-18 draw in 2006.
Wales’ two previous defeats to Italy had come in Rome, in 2003 and 2007, and Pivac felt the officials played a part in an ignominious third at home.
Replacement prop Wyn Jones thought he scored a second-half try, but the officials were unconvinced he had grounded the ball under the posts.
Pivac said: “It’s in the wording, isn’t it? On field no-try. I thought it looked as if he got across the line.
“He’s a big man and the ball’s underneath him, so if it didn’t touch a blade of grass I’d be very surprised.
“When you ask an inexperienced TMO to have a look at it, but it’s onfield no try, her decision was no try. But we have to be better to get across the line.”