Italy led 15-0 at the break after an utterly dominant first-half showing but Wales responded with gusto after the interval with four unanswered tries and seal a famous evening in Cardiff.
It was one-way traffic early on, with the Italian scrum well on top and Marcos Gallorini and a penalty try sent the visitors into the break in control.
But Wales looked a different team after the break, with their energy and purpose in attack too much for Italy to handle as Harry Thomas, Harry Beddall, Kodie Stone and Matty Young all crossed in an electric second period to secure what appeared at times an unlikely victory.
It was the visitors who made the brighter start, forcing a number of early penalties before almost forcing themselves over the line only to be denied by superb defending from Morgan Morse.
But Martino Pucciarello was able to put Italy three in front moments later, slotting over from close range after his side drew another penalty.
Italy continued to rack up penalties in favour, in large part thanks to their superiority at the scrum and quickly marched their way into the Wales 22 but the hosts were able to clear their lines.
Yet the pressure remained, this time Italy running the ball through the hands to try and set Lorenzo Elettri free and Gallorini led the forward drive towards the try line.
Another penalty brought another series of scrums, and this time Italy took advantage, with the impressive Gallorini powering his way over for the game’s opening try after 16 minutes.
But Wales responded with their first real attack of the game, with a driving maul forcing the Italian defence back to their own five metre line but sublime work at the breakdown allowed Luca Bellucci to turn the ball over almost on his own try line.
Those first Welsh forays forward heralded a more even period of play before Italy soon found themselves back in the 22, only to be halted by a terrific turnover from Harry Beddall.
But Italy regrouped and returned, relentlessly probing the Welsh try line but were held up until the penalty count eventually told, with a penalty try awarded as Italy’s maul began to march over the whitewash and Josh Morse was sent to the sin bin.
Italy went into the break 15-0 to the good but it was Wales who started the second period on the front foot and they got themselves on the scoresheet and back into the game just seven after the restart.
Pressure in the Italian 22 saw Samuele Mirenzi head to the bin, and Welsh numerical advantage was immediately converted with a rolling maul powering over the line and Harry Thomas dotting down.
The Welsh comeback continued with a second try on the hour mark, more relentless pressure yielding a string of penalties from which the home side returned to their effective rolling maul for Beddall to dot down, and Harri Ford added the extras to cut Italy’s lead to just three.
The Cardiff crowd began to roar as they sensed a real opportunity for their side, with the penalty count now racking up against the visitors.
And Wales took the lead with 13 minutes left to play as debutant Kodie Stone dove over in the corner after outstanding work from Macs Page to rescue a loose ball and ride a number of tackles.
Wales now led by four but were clearly in the mood for more and drove Italy straight back to their own try line, with Ford eventually releasing Matty Young to crash over.
The lead was extended further to 12 thanks to a late penalty by Ford before victory was seen out with some resolute defending.
