Now in their late teens, the boys and their coach, Mr Ekkapol Chantawong, descended into the spotlit chambers of the Tham Luang cave complex to pay tribute to the thousands of people who worked for 18 days and nights to get them out.
The "Wild Boars" team had entered the caves in June 2018 and were trapped when rains flooded the complex, emerging after a daring international rescue operation to global acclaim.
"If it weren’t for these people we wouldn’t have survived, and wouldn’t have been alive this day," Mr Ekkapol said.
"I’d like to say thank you to all of you from the bottom of my heart."
But the joyful anniversary was tinged with sadness following the death of 17-year-old captain Duangpetch Promthep, who died while on a football scholarship in Britain earlier this year.
His former teammates each laid white flowers at a memorial image of him outside the caves, surrounded by crowds in the bright sunlight and vivid jungle flora.
A video tribute was also played inside the cave for ex-Chiang Rai governor Narongsak Osatanakorn, who won plaudits for his handling of the incident, and who died last month.
"We must not forget the efforts of everyone involved in the rescue mission, especially of those who are no longer here with us," said Mr Varawut Silpa-archa, minister of natural resources and environment.
Offerings were also made to Jao Mae Nang Nong – a legendary princess said to be the spirit of the caves in which she supposedly died, and who was frequently invoked for strength during the rescue.
Miraculous rescue
The boys were on a day trip to the cave complex on June 23, 2018, when heavy rains flooded the complex via underground waterways.
They were feared dead until two British cave divers negotiated a series of narrow waterways and corridors and found them on July 2, trapped in a deep chamber, 4km from the entrance.
The next hurdle was safely moving the boys and their coach out of the caves.
In a highly risky operation, they were sedated, dressed in wetsuits and breathing apparatus, and hauled through the complex by foreign cave hobbyists, expert divers, and a team of Thai navy SEALs including Saman Kunan, who died during the rescue.
Despite the odds, the boys and their coach all made it out alive.
Mr Adul Sam-on, one of the footballers who shot to fame after he thanked the divers who found them in English, was granted Thai nationality following the rescue, as were his coach and two teammates.
Speaking on Monday, the now-19-year-old said he had just graduated from high school in the United States, and would shortly be attending university.
While there has been a steady stream of books, TV series, and film adaptations of the rescue, the boys themselves have mostly kept out of the limelight.
Mr Mongkol Booneiam, known as Mark, said he still lives – and plays football – in a nearby village.
"If I have free time then I’d try to go play," he said.