Fiji put in a dominant second-half performance to silence the Hanazono Rugby Stadium crowd and claim a record-stretching sixth Pacific Nations Cup title.
Home hopes were raised when Japan centre Dylan Riley scored a brilliant solo try at the end of the first quarter of the final, but Fiji responded in emphatic fashion.
Vuate Karawalevu (twice), Ponipate Loganimasi (twice) and Albert Tuisue each crossed the whitewash as the Flying Fijians surged to a 41-17 victory and their first Pacific Nations Cup crown since 2018.
The margin of victory also ensures that Fiji will climb above Australia and into ninth when the World Rugby Men's Rankings are updated at 12 noon (GMT+1) on Monday.
Japan, meanwhile, will slip beneath Samoa, who beat USA 18-13 in the third-place play-off earlier on Saturday, to 14th in the rankings.
Fiji 41-17 Japan
Seungsin Lee and Caleb Muntz traded early penalties before the final exploded into life with a moment of magic from Brave Blossoms centre Dylan Riley in the 20th minute.
Having stepped inside three attempted tacklers and shrugged off a couple more, Riley chipped the ball over the covering defender and won the race to the bouncing ball to dot down.
Lee added the conversion but if the home fans hoped the try would signal the start of a dominant period for Japan, then they were to be disappointed.
Fiji thought they had their first try of the match in the 31st minute as Inia Tabuavou crashed over from close range, only for TMO Damon Murphy to spot an earlier knock on from Tuisue.
The Pacific Islanders had to wait less than 60 seconds to cross the whitewash however, and centre Tabuavou was again involved. His skilful hack on, after Japan captain Harumichi Tatekawa's grubber had been blocked by Eroni Mawi, fell perfectly for winger Vuate Karawalevu to kick on and score. Muntz added the extras to level the scores.
That is how the score remained at half-time, although the hosts headed into the changing rooms a player light after hooker Mamoru Harada was shown a yellow card.
Japan stood firm in their 10 minutes with 14 players, albeit Fiji number eight Elia Canakaivata had a try ruled out for an earlier obstruction. And as the half wore on, Fiji's bench proved decisive as their replacements made a real impact in the final 30 minutes.
Player of the Tournament Muntz stretched the Fijian lead with another penalty before a lovely team move created the space for replacement winger Loganimasi to score in the right corner.
Fly-half Muntz converted from out wide to give his side a 10-point lead and then produced a stunning 50/22 to give Fiji an attacking platform when they had been on the back foot.
Minutes later, Tuisue burrowed over from close range despite the attention of several Japanese defenders before an outrageous offload from flanker Kitione Salawa released Karawalevu to score his second of the night.
Loginamasi stepped around an attempted tackle from full-back Lee to add an exclamation mark to his impressive performance off the bench, before Japan winger Malo Tuitama gave the home crowd something to cheer with a consolation try late on.
Samoa 18-13 USA
Samoa came from behind to secure their first win against USA in nine years and claim third place in the reimagined Pacific Nations Cup.
Friday was the ninth anniversary of the Pacific Islanders' last victory in this fixture, a 25-16 win at Men's Rugby World Cup 2015, and it looked as though that long wait would go on in the opening exchanges at Hanazono Rugby Stadium.
Luke Carty opened the scoring with an early penalty and then put the Men's Eagles into a 10-0 lead with less than eight minutes on the clock, converting Toby Fricker's try.
USA full-back Fricker had capitalised on a poor Rodney Iona clearance to take a brilliant catch high above the would-be chasers and run in unopposed. But that was about as good as it got for Scott Lawrence's side.
Iona made amends before half-time, converting a brace of penalties to draw Samoa within four points. Carty missed a late long-range penalty attempt of his own to leave the score at 10-6 at the break.
And that provided the platform for Samoa to overhaul the Men's Eagles as Iakopo Petelo-Mapu powered through a series of tackles to score a sensational individual try within two minutes of the restart.
Iona added the simple conversion but USA were soon back level as Carty struck another penalty.
However, as the match looked to be heading towards a draw, Jason Daam was shown a yellow card for collapsing a Samoan maul five metres out.
And with the second row in the sin bin, the Samoan pressure eventually told with three minutes left as Melani Nanai went over in the left corner.
-World Rugby