Organisers were set to allow 20,000 fans into the May 9 meet, according to Kyodo news agency, but tougher restrictions imposed by the Tokyo city government this month have forced a rethink.
Earlier, Anett Kontaveit of Estonia set up a second-round tie with third-seed Sofia Kenin of the USA after a 6-2, 6-3 win over German qualifier Julia Middendorf.