At stake is potential access to the lithium reserves of Bolivia's Salar de Uyuni salt desert and the huge advantages that it would confer as nations jostle to gain early supremacy in the manufacture of electric cars.
However, the extraction rights that Japan has won are not exclusive and Bolivia is keen to continue stoking what has been, for the impoverished South American country, a uniquely lucrative and arbitrary beauty contest of rich Asian nations.
Yuko Yasunaga, director of mineral resources at the Japanese Trade Ministry, said that it remained likely that the South Koreans and Chinese might still be invited to participate in the same experiment or to conduct their own.
'I would say that (this deal) puts us in the paddock for the race,' he said.
The deal may represent a psychological setback for South Korea, which signed a memorandum of understanding in September that appeared to make Seoul the most-favoured partner.
That agreement was signed after an onslaught of diplomatic flattery and financial support by South Korea, but even its architects admitted that it did not 'definitely separate us from rivals in acquiring development rights'.
Bolivia may even be widening the field of potential partners just as it signs its deal with Japan.
Sources at the main Salar de Uyuni site in the central Andes said that over recent weeks delegations of scientists and mining engineers had arrived in the arid Bolivian Altiplano from Iran, Brazil, Russia and Canada with a view to offering their own partnership deals.
France and Finland have emerged previously as possible rivals to the Asians. As the scramble for resources has intensified, attempts to secure development partnerships with Bolivia have grown more elaborate and desperate - before even a single ounce of commercially viable lithium has left its brine lakes.
All three Asian governments have spent recent months bombarding the mercurial President Morales with the full arsenal of diplomatic and commercial entreaties. They have offered everything from schools and sewage works to development cash and state visits.
The deal struck between the Bolivian Government and Japan's state-backed consortium of academic institutions and companies gives the Japanese 'participation rights' in a test project. The 18-month experiment aims to demonstrate that lithium can be extracted at Uyuni on a commercial scale and that the Japanese technology is, as its developers claim, the most effective way of achieving that.
Nobody is keener to start the extraction process than Mr Morales, but his country lacks the technology to develop the lithium resource on its own. He has used this situation, according to companies in Tokyo involved in the project, to make potential partners as generous as possible.
In one of his many shifts of position, Mr Morales declared last month that he wanted Bolivia to have its own lithium battery industry - an ambition, some say, that stretches the limits of logic or practicality.
But while Mr Morales may be difficult to deal with, his suitors are effectively forced to accept his sudden changes of heart. Unless a viable alternative to lithium is found for batteries, the most bullish projections for electric car demand will require the resources of Bolivia to be tapped soon to take some of the supply strain off Chile, the largest existing supplier.
Japan, which imports about 86 per cent of its lithium from Chile, is desperate to prevent global control of lithium slipping into Chinese hands. Japan's high-tech industry is already threatened by China's dominance of rare earth metal production: Beijing's recent diplomatic row with Tokyo allowed China to demonstrate that power when a sudden trade embargo in September starved Japan of vital minerals.