Continuing his inspired run from qualifying, Hijikata lit up the indoor Plenitude Arena to bring down Djokovic 2-6 6-3 6-3 to surge into the Paris Masters third round.
In sending Djokovic packing under a barrage of baseline winners, the world No.83 joined Alex de Minaur, Nick Kyrgios and Lleyton Hewitt as only the fourth Australian to conquer the mighty Serb and further enhance his career-best season.
Victory was the 28-year-old's fourth top-20 scalp of 2026, having never previously claimed one, and thrust Hijikata to within one win of a fresh career-high ranking inside the world's top 60.
Yet the Sydneysider almost withdrew before a ball was even hit on Thursday (AEDT).
"I just cooked my neck a bit yesterday and, to be honest, it wasn't feeling great last night or this morning," Hijikata said after becoming the lowest-ranked player this year to topple seven-times Paris champ Djokovic.
"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."
Djokovic reached the Australian Open final in January and then won his 102nd tour-level title in Beijing last month, but the 39-year-old could not extend his 2026 season further in France.
Defeat scuttled the 24-time grand slam winner's chances of qualifying for the season-ending championship, an event he's also won seven times.
"Disappointment, obviously, losing a match that I felt like I was dominating for a set and a few games," Djokovic said.
"Then he was switched on. I wasn't serving as well in the second set. He was just playing out of his mind, honestly. He was not missing, keeping the ball low. It was a terrific performance.
"Nobody loves losing. It's just another match, but I should've won this match. I played well in the first set and then completely lost control."
Hijikata next faces Tomas Martin Etcheverry, the Argentine who crushed Alex de Minaur's hopes of making Turin for a third straight year with a 7-6 (7-2) 6-3 victory over Australia's world No.9.
