A day after Japan staged a historic upset over Ireland at the Rugby World Cup, England forwards coach Steve Borthwick said Sunday he was "not surprised" at the result, adding that he was pleased at how the Brave Blossoms built on the legacy he helped create at the 2015 tournament.

"Not surprised," said Borthwick, a member of Japan's coaching staff at the 2015 tournament. "They play smart in a very well coached team... The tenacity in which they play, the tenaciousness they have -- very impressive in that regard."

While many expected Ireland, who came into the tournament as world No. 1, to come out as victors following the match in Shizuoka, Jamie Joseph's side pulled off a 19-12 victory and improved their chances of reaching the knockout stage for the first time.

The win came four years after Japan defeated two-time world champions South Africa in what came to be known as the Brighton Miracle, considered one of the largest upsets in the history of the sport. Borthwick was the forwards coach for the team led by current England head coach Eddie Jones.

Borthwick said Japan's mentality has improved drastically since the 2015 tournament, in a way in which they believe they could win against even against higher-ranked opponents.

(Steve Borthwick)

"I think that certainly a big area of development prior to 2015 was the team believing they could win and expectation to win," he said. "But now Japan go into these games expecting to win. That's great credit to what the coach and the team have done with them."

While the shocking victory over South Africa introduced rugby to many Japanese who were unfamiliar with the sport, Borthwick said Japan's strong run at this tournament will have an even bigger influence on the public.

"You saw that the team, the team in 2015, looked a lot at how they can bring the popularity of the sport and felt the responsibility for the sport in general in Japan," Borthwick said. "What 2015 did undeniably was to lift rugby again within Japan... I'm sure yesterday's game has been a step forward in that regard."

"For the home nation, host nation, to have a game like yesterday, a result like yesterday, without question helps."

Japan sit atop Pool A with nine points after opening their World Cup campaign with a 30-10 win over Russia. They will play Samoa on Saturday before facing Scotland on Oct. 13.

"The more and more people get exposed during this tournament, I think it can help the game grow even better," Borthwick said.

Related coverage:

Rugby: Japan cannot be complacent after upset over Ireland: Leitch