Head coach Eddie Jones said Japan had taken "a good step forward" by beating Fiji 20-15 in a gritty performance to win the Pacific Nations Cup in Tokyo on Saturday.
Jones's side gained a measure of revenge on the Fijians after losing to them in the previous two Pacific Nations finals, settling a tight game when substitute Samisoni Tua crashed over in the 72nd minute.
It gave Japan their first title since 2019 in a competition that has undergone several changes of format.
Japan have lost a number of close contests over the past year and Jones said his team would benefit from nailing the victory.
"We couldn't get our attack going but what I thought we did get right today was our intensity in our defence," the Australian said.
"I've never played against a Fiji side that made as few line breaks as they did.
"That's a good step forward for us."
Canada earlier claimed third place, edging the United States 19-16.
The final was played on a rain-slicked pitch that made it difficult for Japan to get into their fast-passing groove.
"We didn't get our attack going at all, so we relied on our set piece to get us points," Jones said.
"We're an attacking team so that's disappointing, but when I look at the conditions, the conditions were difficult."
COSTLY CARD
Fiji were looking for their third straight Pacific Nations title after beating Japan in Osaka in 2024 and in Salt Lake City last year.
Their chances took a hit when prop Mesake Doge was yellow-carded midway through the first half.
Fiji interim coach Senirusi Seruvakula said temporarily going down to 14 men was an "unexpected" setback.
"We were defending for more than 20 minutes," he said.
"It was one of the areas that was killing us."
Fiji scored the first try when Virimi Vakatawa barrelled through several tackles to touch down in the 11th minute.
Doge was then sin-binned and Japan capitalised when Mamoru Harada scored in the 22nd minute.
Fiji hit back five minutes later with a try from captain Tevita Ikanivere.
The Fijians held on to their slender lead in a scoreless start to the second half, but Japan's pressure eventually paid off when Ben Gunter stormed over the line in the 58th minute.
Fiji evened the score with a penalty but Tua had the last word when he barged over for Japan's third try.
The Fijians went into the tournament after a chastening time in the inaugural Nations Championship this year, conceding more than 140 points in defeats to Wales, England and Scotland.
Captain Ikanivere said his team had made improvements since then.
"You can see the effort out there today and the physicality, we talked about coming out to be brutal," he said.
"We just gave away too many penalties in the breakdown area."