Samoa wing Malu Falaniko finished with 20 points as his side defeated U20 World Championship hosts Italy 30-24 in Calvisano.
Italy started brightly when their scrum powered over the ball and Renato Giammarioli was on hand to push past the Samoan tacklers to reach the try line, with Matteo Minozzi converting for a 7-0 lead.
Italy couldn't rest on their laurels however as Samoa hit straight back, fly-half Orbyn Leger scooping up a loose pass and stepping his way through the defence to tie things up after Falaniko's conversion.
The left winger added a penalty not long after to put Samoa ahead for the first time and he was then on the end of a sweeping attacking move. The Italian defence couldn't cover the overlap as Chase Tiatia and Pisi Leilua released Falaniko for the Samoans' second try.
Falaniko's kicking remained perfect as he added the conversion before Italy responded with a close-range try for Jake Polledri but Samoa had the final word of the half when Falaniko added his second penalty to make it 20-12 at the break.
Urged on by the home crowd Italy's pack rallied and put them ahead with two quick tries, the first a well-worked lineout move finished by Edoardo Ferraro before the replacement Davide Zanetti crashed over off the back of a rolling maul to make it 20-24.
Falaniko's boot cut the gap to one point before Samoa, after turning down easy three-pointers for the lead, eventually went in front when Ben Tuiomanufifi scored after Riccardo Raffaele was charged down.
That score set up a tense final few minutes for the Italians as they chased the game, but the hosts lost their composure at the death as Samoa clung on for a famous win.
Tries: Leger, Falaniko, Tuiomanufifi
Cons: Falaniko 3
Pens: Falaniko 3
Tries: Giammarioli, Polledri, Ferraro, Zanetti
Cons: Minozzi 2
Samoa: 15 Chase Tiatia, 14 Pisi Leilua, 13 Jonathan Faauli, 12 Josh Ioane, 11 Malu Falaniko, 10 Orbyn Leger, 9 Jonathan Taumateine, 8 Giovanni Kuefner, 7 Uini Fetalaiga, 6 Jordan Jackett, 5 Ezra Meleisea, 4 Ben Tuiomanufili, 3 Mike Tamoaieta, 2 Ieremia Mataena, 1 Junior Halafuka.
Replacements: 16 Kemble Frost, 17 Jarred Adams, 18 Marco Fepulea'i, 19 Darren Tiumalu, 20 Gordon Langkilde, 21 Melani Matavao, 22 Pepesana Patafilo, 23 Mika Tapili.
Italy: 15 Luca Sperandio, 14 Tommaso Beraldin, 13 Lorenzo Casalini, 12 Enrico Lucchin, 11 Lorenzo Masato, 10 Matteo Minozzi, 9 Riccardo Raffaele, 8 Renato Giammarioli, 7 Jake Polledri, 6 Marco Lazzaroni, 5 Samuele Ortis, 4 Ugo D'Onofrio, 3 Andrea Cincotto, 2 Edoardo Ferraro, 1 Paolo Buonfiglio.
Replacements: 16 Luhandre Luus, 17 Dino Dallavalle, 18 Federico Pavesi, 19 Davide Zanetti, 20 Matteo Cornelli, 21 Matteo Ferrari, 22 Maicol Azzolini, 23 Giacomo De Santis.