England beat earnest Japan in gritty Rugby World Cup performance
The Japanese impressed in the first period, despite the English taking a 13-9 lead in at the break.
England, improved enough after a talking to from manager Steve Borthwick, finished the job in the second half.
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Speaking after full time, player of the match George Ford said: "We are just really happy with another win tonight. We knew it was going to be tough and Japan challenge you in different ways.
"We knew it would be that third or fourth quarter we could pull away a bit, but we are delighted to get the win.
"It was probably not the prettiest watching it. It's really hard to play with the ball in these conditions, these late kick-offs are dead greasy, but we got there in the end."
'Decent header'
Courtney Lawes, who was standing in as captain for the suspended Owen Farrell, told BBC Radio 5 Live: "Full credit to Japan. We knew they would put up a fight.
"It was so greasy, but we did well to come away with five points. I can’t ask for much more."
Lawes showed his initiative in the second period, continuing to play and scoring a try after the ball struck teammate Joe Marler. Japan's players, however, stopped and just watched it happen.
A review by the match officials for a possible knock-on ruled in England's favour, which proved to be a turning point.
"That was a decent header from Joe, sometimes the luck falls in your favour so I will take it.
"We wanted to play good rugby but conditions were tough. We saw what we wanted to do, but we will stick with it."
England are next in action against Chile on September 23rd.