Team GB made it two wins in a row over beating Japan 21-19 in session two
A brace from James Rodwell gave the men a 14-7 lead at the break
Marcus Watson's converted score won the game for Gb with only seconds to go
Britain face New Zealand at 16:30 tomorrow in the final match in Pool C.
The top two sides in each of the three pools go into the quarter-finals, plus the two best third-placed teams.
Team GB, who
won their opening match against Kenya, didn't take long to get going as some tremendous footwork from
Dan Bibby released
James Rodwell, who turned on the afterburners for try time.
Tom Mitchell then added the extras, 7-0.
Powerhouse Rodwell then added a second straight off the kick off, again finishing in style under the posts. Mitchell then converted to stretch Team GB's lead to 14 points.
The brave blossoms nevertheless got back into the clash on the edge of half time when Lomano Lemeki sliced through Great Britain's defence like a warm knife through butter, 14-7.
Kenki Fukuoka flew down the left wing to bring Japan level but late on Newcastle Falcons winger Marcus Watson burst in for what seemed surely the winning try.
The Japanese sevens team however never give up, with Lomano Lemeki touching down in overtime. Kameli Soejima pulled the conversion wide though, which was a get out of jail free card for Great Britain as they edged to victory.