Having taken the first two sets, they offered up the third to a quick and agile Japan, before exerting their height advantage again in the fourth.
They are now top of Pool A and, with only Italy capable of catching them in the race for top spot, the final-game match-up between the two promises plenty.
The main difference today was in the block, with Ekaterina Gamova killing the ball five times – just once less than Japan managed combined.
Gamova left the court with 29 points and was ably assisted by Nataliya Goncharova with 26. Saori Kimura top-scored with 23 for Japan, sharing the honour with Saori Sakoda.
Japan end their group with a clash against host nation Great Britain and look set to have to settle for third place, with Italy and Russia too far ahead to catch.