The gargantuan 28-26, 23-25, 25-23, 23-25, 18-16 tussle lasted two hours and 15 minutes and when it eventually ended, the outpouring of emotion from both sides could not have been more contrasting.
Japan's players stormed the court, piling on each other, while China - the 2004 winners - saw players slump to the floor, some of them in tears.
In the end China were looking for flights home, taking a cumulative two points fewer than their opponents.
The statistics for both sides could hardly have been tighter. They won three points each on serve and 82 on spike, with Japan blocking 11 times and China 10. The latter made one unforced error more.
Yukiko Ebata and Saori Kimura equally shared 66 points for Japan, while for China Ruoqi Hui scored 26 and the incredible Yimei Wang set aside her injury worries to register 22.
Japan's reward is a meeting with either defending champions Russia or Brazil, with a first final since 1976 beckoning.
Their coach, Masayoshi Manabe, said: 'We co-ordinated really well and the players worked really well together. Both teams were so nervous in the final set, but Japan had just a little bit more.'
China coach Yu Juemin said: 'This match is the first time we have had a difficult match at London 2012. We had a lot of pressure, we really wanted to win, so it caused a lot of problems.
'But we targeted the quarter-finals and we made that aim, so we have taken an important step in our progress.'