De Minaur's 7-6 (7-2), 6-3 defeat to Argentine Tomas Martin Etcheverry ended his hopes of an automatic qualification spot at the end-of-year ATP Finals in Turin, where he has competed for the past two seasons. The world No.9 was already in a tight race with Spanish phenom Rafael Jodar for the final qualifying spot, a contest rendered moot when both exited in the second round. The ATP corrected a scoring discrepancy that left De Minaur 49 points behind Jodar.
De Minaur remains the first alternate, but Taylor Fritz and Tommy Paul could surpass him with deep runs in the French capital.
Hijikata came through qualifying and dispatched Italy's world No.21 Luciano Darderi for the third time this year before defeating the 24-time major champion 2-6, 6-3, 6-3. He joined de Minaur, Nick Kyrgios and Lleyton Hewitt as Australians to have beaten the Serbian great.
The Sydneysider considered pulling out of the match. "I just cooked my neck a bit yesterday and, to be honest, it wasn't feeling great last night or this morning," he said. "But I guess a bit of adrenaline kicked in, and I was going to do whatever I could, so I'm glad about my performance."
The loss also rules Djokovic out of playing in Turin, which he had hoped to attend after skipping the past two editions. At 39, the Serbian had slipped outside the top 10 with a lighter schedule and has become more vulnerable to the kind of upsets that were rare in his prime. The day was marked by major surprises, with world No.1 Alexander Zverev, Daniil Medvedev, Frances Tiafoe and Learner Tien also losing in the men's draw.
De Minaur rallied late in the season to reach finals in Beijing and Vienna, but failed to make a grand slam quarter-final outside the Australian Open. The seven-time grand slam quarter-finalist rose to a career-best No.5 in July but now faces growing competition from younger players including Ben Shelton, Jodar, Flavio Cobolli, Arthur Fils and Jakub Mensik. Cobolli defeated de Minaur at Wimbledon.