Boks beware: 'Scary' how good Japan can be, warns sleepless Leitch

After a sleepless night replaying Japan's historic Rugby World Cup victory over Scotland in his head, captain Michael Leitch has warned quarter-final opponents South Africa that lightning can strike twice.

The hosts won a cliffhanger 28-21 in Yokohama at the weekend to top Pool A and reach the knockout stage for the first time, exorcising the ghosts of 2015 when they toppled the Springboks and won two more games but failed to advance.

Japan's talismanic skipper admitted Monday he was still a little dazed after such an emotional night.

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"I was in my bed about 1:30 and haven't actually slept -- I've been awake the whole time, so I'm a little bit slow today," said Leitch.

"Looking back, even since 2011, this team has grown so much -- and it's scary to think how far this team can grow," added the marauding flanker.

"The last four games, we've been getting better each time and our confidence is growing."

Japan, once pulverised 145-17 by New Zealand at the World Cup, defied odds of almost 50/1 to finish top of their pool ahead of runners-up Ireland and the Scottish, who fly home early.

South Africa battered Japan 41-7 in a World Cup warm-up last month, but Leitch insisted that would have no bearing when the teams meet in Tokyo next weekend.

"Our self-belief has increased game by game," said Leitch, rippling muscles bulging through his Japan uniform, and looking slightly out of place at a press conference held in a hotel chapel.

"It's going to be a very tough game against South Africa but we've prepared for this," added Leitch, before being ushered out to make way for a wedding.

"The most important thing is to start from zero and build again, piece by piece."

- Iron will -

Sunday's victory carried echoes of 2011 when the Japanese women's football team lifted the World Cup, embodying the iron will of a nation recovering from the deadly earthquake and tsunami earlier that year.

As 67,000 fans erupted with joy at the final gong on Sunday, Leitch took a moment to pay tribute to the victims of a violent typhoon that claimed more than 30 lives over the weekend, with the death toll expected to rise.

"Everyone is suffering with the typhoon," he said, after Japan avenged the 45-10 defeat by Scotland that cost them a place in the last eight four years ago. 

"This was for all of you guys."

On Monday, pictures of Japan's history-making heroes were splashed all over the country's newspapers with jet-heeled wingers Kenki Fukuoka and Kotaro Matsushima -- who Joseph calls his "Ferraris" -- grabbing many of the headlines.

Fukuoka scored two superb tries to win man of the match, collecting his trophy from Japanese tennis star Naomi Osaka.

"We wanted to make history and it's amazing to actually achieve that," said Fukuoka, who scored Japan's try in the 19-12 upset over Ireland.

"Now we turn to South Africa and we have nothing to lose."

Matsushima added: "This is worth all the hard work and sacrifice -- I'm just trying to bring a little oomph to the team."

Veteran lock Luke Thompson has described next week's quarter-final is a "free hit" for Japan, who have climbed to seventh in the world rankings.

"Four years ago we were able to sneak up on South Africa," he said.

"Now it's a completely different situation. No one expects us to win again -- but we believe."