The last sellout for a Sydney rugby league Test came in 1974, when 55,505 spectators watched Australia play Great Britain at the SCG.
Thursday's World Cup opener is on course to draw the city's largest Test crowd in more than five decades.
Officials said on Tuesday that ticket sales were just below 40,000 for the match at Allianz Stadium, which holds 42,500.
The biggest international attendance in Sydney during the NRL era is 34,571, recorded at the 2008 Centenary Test between New Zealand and Australia at the SCG.
Thousands of New Zealand supporters have bought tickets, encouraged by hopes that Stacey Jones' squad can spring an upset in the opening match.
Ronnie Mulitalo and the visiting fans are expected to bring plenty of heckling to Thursday night's game.