The plan was attacked as too risky, but brave rescuers forged ahead to save the first four of 12 boys trapped in a Thai cave as torrential rains hit the region.
The youngsters, aged between 11 and 16, faced a dangerous and frightening journey out of the flooded Tham Luang cave system on Sunday.
Their toughest challenge came near the beginning of the treacherous 3km route, during a terrifying 200m dive.
Read more: Live: Weakest boys safe, cave rescue could take four days
The boys had to squeeze through a narrow, 38cm hole in the rock known as a "choke point".
Each boy was accompanied by two divers — one in front and one behind. But at this choke point, where an upward slope was followed by a sharp bend downwards, they would have to go it alone, climbing out of the water and over the peak before descending back into its murky depths.
It was hazardous even for the experienced divers with them, who needed to remove their bulky scuba tanks to fit through.
One reporter on the scene described the gap as "barely bigger than a standard school ruler or the size of your head".
Many of the boys trapped in the cave with their soccer coach cannot even swim, and some are weak and exhausted from malnourishment. Rescuers have spent the past few days trying to teach them basic diving and breathing skills.
An Australian doctor's triaging of 12 boys trapped in a cave in northern Thailand may have led to the rescue of four of the weakest children first.
The initial plan was to bring the strongest out first.
But after Adelaide cave diver and anaesthetist Richard Harris, 53, assessed the youngsters and their coach that strategy appears to have been reversed, Thai media has reported.
Thirteen divers entered the cave at 10am Sunday local time (1pm AEST) — some heading straight for the trapped group and others taking up stations along the string of flooded chambers.
Ten rescuers headed to the boys in chamber nine and to the junction at chamber six, while the others headed to support positions shortly afterwards.
Each boy had to wear a full scuba mask, wetsuit, boots and a helmet as they made their way through the dark and perilous passageways.
They were strapped to the leading diver by a tether and dragged along by their "buddy", who carried two tanks and shared oxygen with the boy as they followed a submerged rope.
A second diver followed the pair through the cold water and airless chambers that have already claimed one life.
The foreign divers and five Thai divers entered the caves after an Australian doctor gave the all-clear. Locals were required because none of the foreigners speak Thai and communication before and during the dive was key.
Additional rescue personnel, including divers from Thailand, the US, Australia, China and Europe, were stationed between the third chamber and the entrance, where the boys would have to use a rope to traverse challenging terrain.
The first two boys successfully completed their mission at 5.40pm and 5.50pm local time (8.40pm and 8.50pm AEST), with another two following two hours later, ten minutes apart.
There were hopes another two boys might make it out, but the rescue had to be placed on hold for 10-20 hours while oxygen supplies were replenished.
As morning breaks, the remaining eight boys and their 25-year-old soccer coach will be hoping they, too, are as successful as the first four.
And they have the whole world hoping with them.
Simone White, 28, is the fifth tourist to have died after becoming ill last week.