Errors in two of her five dives saw British record holder Powell finish in 20th place with 287.30 points.
Gladding, who said it was "touch and go" whether she competed after discovering a prolapsed disc in her neck last week, finished 19th.
China's defending champion Ruolin Chen leads the standings with 392.35 points.
Chen is hoping for her second title of the Games having won synchronised 10m gold alongside Hao Wang last week.
Gladding, who suffered a life-threatening injury last year after striking her head on the platform whilst competing in Russia, needed a fitness test on Wednesday to prove she was able to compete in the 10m preliminaries.
"I've had problems with my neck since my accident and it really flared up quite badly," said Gladding, who will consider her future in the sport after undergoing neck surgery in the next couple of weeks.
"It was touch and go whether it was safe to dive.
"I've been in tears throughout the last week, but I couldn't have given any more."
The 18 semi-finalists will return on Thursday at 10:00 BST to compete for a place in the evening's final, which gets under way at 19:00.