The Italians went into the Pool B encounter at Waitakere Stadium in Auckland with five points under their belts after an opening weekend bonus-point win over USA and a defeat to Canada.
Going into this game they were ranked fifth in the World Rugby Women’s Rankings powered by Capgemini while Japan – on zero points before kick-off – were 12th.
However, the latter gave it everything here and were 14-8 down until the 79th minute after a great showing and they can be proud of what they have brought to the tournament, although they are now going home.
It is Italy that are through to a Rugby World Cup quarter-final for the first time and afterwards their loose-head prop Silvia Turani said: “A win is a win and the most important thing here is that we responded to things within the game and found a way to get the victory.
“It means a lot for us to get through to the quarter-finals and we want to inspire people back home in our country.”
It was Italy who took the lead in the ninth minute when winger Maria Magatti went over for the opening try. Centre Michela Sillari could not convert and it was 5-0.
Any thoughts that that score would open the floodgates proved unfounded as Japan gave as good as they got.
And, indeed, it was the Sakura Fifteen who scored the next points on the half-hour mark.
Flanker Kyoko Hosokawa scored a try which fly-half Ayasa Otsuka just failed to convert and things were all square at 5-5.
Three minutes before half-time Italy regained the lead when a Sillari penalty gave them a slender 8-5 advantage at the break.
Into the second half the Japanese side made an early replacement as Megumi Abe was replaced by Moe Tsukui at scrum-half and the use of their replacements was to become a common theme during that period.
However, before any more changes were made, Otsuka levelled things up with a 49th minute penalty.
From 8-8, Italy knew they needed a big last half hour to keep their hopes of progressing alive and, although they never quite hit top form in the face of good defence by Japan, they did enough to get the win.
Sillari kicked a second penalty of the day in the 55th minute and then, eight minutes later, Japan were reduced to 14 players.
Winger Komachi Imakugi was yellow-carded by referee Maggie Cogger-Orr for head-on-head contact with Italy back-row Giada Franco while trying to make a tackle.
While she was off the pitch, Sillari kicked a third penalty and then, with Japan back to 15 players, Italy made sure of the victory when hooker Melissa Bettoni went over for a try. Sillari converted with 60 seconds left on the clock as it finished 21-8.