Fiji led 17-3 at half-time, despite having centre Jale Vatubua and captain Akapusi Qera sinbinned, and stretched the lead to 24-3 while prop Eroni Mawi received a yellow card early in the second spell.
Kini Murimurivalu, Ben Volavola, Henry Seniloli and Vereniki Goneva scored tries for the defending champions, with Volavola adding two conversions.
With 20 minutes remaining Samoa started to overcome their high error count and began to pressure Fiji.
Scrumhalf Melani Matavao, flank Jack Lam and replacement scrumhalf Dwayne Polataivaia all scored in the closing quarter but one missed conversion denied them a draw.
Tries: Vereniki Goneva, Kini Murimurivalu, Henry Seniloli, Ben Volavola.
Cons: Volavola 2
Tries: Jack Lam, Dwayne Polataivaia, Melani Matavao.
Cons: Tusi Pisi, AhseeTuala.
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