Padua - Tonga's Tane Takulua capped a superb all-round display by slotting over a last-minute penalty to seal a 19-17 win over Italy in a see-saw Test in Padua on Saturday.
The Newcastle scrumhalf kicked four penalties and converted Siale Piutau's 51st-minute try as the Pacific islanders repeatedly came from behind to upset a side two places above them in the world rankings.
Lorenzo Cittadini and Tommaso Allan ensured Italy won the try count two to one. But the failure to take numerous opportunities combined with some ill-disciplined defending to ensure a painful comedown from last weekend's historic win over South Africa.
Head coach Conor O'Shea admitted Italy's level of performance had slipped from the standard set against the Springboks.
"Credit to Tonga, they never went away but our execution was not good enough today and our discipline let us down," he said.
"We let slip two or three opportunities in the first half when, had we taken them, it would have been game over."
Tonga spurned an early chance when Takulua pushed a third-minute penalty wide for what was to be his only miss of the day.
But Italy were soon dominating territorially and their pressure paid off after 12 minutes when giant prop Cittadini spun off the outside of a maul from the lineout and powered through Takulua's last-ditch tackle to touch down in the corner.
Carlo Canna converted and Tonga suffered another setback when number eight Tevita Koloamatangi was stretchered off after an off-the-ball collision with Italy wing Giovanbattista Venditti.
Replacement Valentino Mapapalangi was only on the field for three minutes before he was yellow-carded for a dangerous tackle but Italy failed to exploit the numerical advantage.
Takulua slotted over a 33rd-minute penalty to reduce the deficit and the first half ended with the Italians defending desperately after prop Sami Panico was sin-binned for a high tackle.
Another penalty from Tukulua cut the deficit to one point and Tonga went ahead when Piutau went over 11 minutes after the restart.
Australian-born centre Luke McLean reclaimed the initiative for Italy, piercing Tonga's midfield with a deft little forward kick that he collected himself before sending replacement flyhalf Allan in under the posts.
Italy looked the more likely winners at that stage and one sweeping move ended with Giulio Bisegni touching down in the corner only to be denied after a video replay established that his boot had strayed fractionally into touch just before.
That set the tone for a dramatic final 20 minutes.
A superb solo break by Takulua saw the visitors win a penalty close to the posts that enabled them to reclaim the lead with the added bonus of seeing Allan banished to the sinbin for his desperate attempt to prevent the marauding scrum from reaching the touchline.
With less than three minutes left, fullback Edoardo Padovani put Italy back ahead but Tonga's final surge proved too strong to resist and Takulua coolly clinched the victory with the final kick of the match.
Tries: Lorenzo Cittadini (13), Tommaso Allan (55)
Conversions: Carlo Canna (14), Tommaso Allan (56)
Penalty: Edoardo Padovani (78)
Try: Siale Piutau (52)
Conversion: Sonatane Takulua (54)
Penalties: Sonatane Takulua (33, 46, 73, 81)