The home swimmers managed to ignore a crowd so enthusiastic they sometimes nearly drowned out the music the bronze-medallists were swimming to, a Chinese piece named "The Yellow River".
Russia won a clutch of perfect 10s for both the technical and artistic aspects of their routine in the team final.
Spain took silver with a routine that included one swimmer rising above the water with hands and feet resting on the heads of four others.
Russia defend synchro gold
The event was overshadowed, however, by the collapse of one of the Japanese swimmers, who after her routine had to be swum to the edge, lifted out of the pool and carried off on a stretcher.
Team officials said later she had suffered breathing difficulties but was conscious and now recovering.
Russia have dominated synchronised swimming since the 1997 World Cup, when they ended the hegemony of the United States and Canada.
Lights off for Spain
Russian champions lead