With the sport making its Olympic debut, tensions were clearly high on a hot and humid day at the Aomi Urban Sports Park, which gave the wall a touch less grip.
The World No.1 slipped twice on the speed wall, meaning she had to settle for 14th place after the first discipline. But the Slovenian Garnbret showed her champion spirit to bounce back with top place in the bouldering and fourth in the lead to seal top spot overall.
Second place in the combined rankings went to Korean lead winner Chaehyun Seo, with home heroes Miho Nonaka and Akiyo Noguchi in third and fourth respectively thanks to their consistent performances across all three disciplines.
They will return to the wall once again for the women's combined final on Friday (6 August).
A slow start on the speed wall
Aleksandra Miroslaw delivered a near world record time of 6.97 on her second run to comfortably take top spot in the speed event.
Her time was 0.01s shy of Yulia Kaplina's mark from last November's European Championships, but it is an Olympic record on the sport's Games debut.
There was also a lifetime best for French speed specialist Anouck Jaubert, who finished in second place with a best time from her two runs of 7.12. Yiling Song of China took third in 7.46.
Nerves appeared to get the better of gold medal favourite and world no.1 Janja Garnbret, who slipped on both of her runs. The Slovenian's best time of 9.44 meant that she had to settle for 14th place.
Garnbret bouldering class shines through
As expected, Garnbret bounced back hard in the bouldering.
The two-time world champion in the discipline put on a total masterclass to solve four problems in four attempts, comfortably taking top spot.
Brooke Raboutou of the United States and Japan's Akiyo Noguchi finished second and third, both completing three out of four problems.
Garnbret's win put her top of the overall qualification rankings, and assured her a place in the Olympic final.
Chaehyun Seo wins lead problem
With everything still to play for in the third and final qualification discipline, Korea's Chaehyun Seo stepped up to take top spot on the lead problem.
The 2019 Asian champion's 40+ performance capped a consistent day, and ensured her place in the final.
Austrian Jessica Pilz managed to make it to the 33+ hold to secure second place, while there was reason to cheer for home fans as Miho Nonaka clinched third.
Garnbret, no doubt conserving her energy for Friday's final, reached the 30 hold to take fourth place.