Williams is one of five centres vying for four spots in New Zealand's World Cup squad, along with Ngani Laumape, Anton Lienert-Brown, Jack Goodhue and Ryan Crotty, who is recovering from a broken thumb.
Folau, who has played 73 times for the Wallabies, raised more than Aus$2 million in just two days through the Australian Christian Lobby to help pay his legal fees.
Fifa president Gianni Infantino had already said that he was determined to push ahead with plans to expand the World Cup in time for the next tournament after hailing France 2019 as 'the best ever'.
Eighth-ranked Stephens, the 2017 US Open champion, lost to Sweden's Rebecca Peterson 6-2, 7-5 while 15-year-old qualifier Gauff fell to Kazakhstan's 84th-ranked Zarina Diyas 6-4, 6-2.