His dream came true Wednesday in spectacular fashion as he won Kenya's historic first gold medal in a field event with an enormous effort in Beijing's Bird's Nest Stadium.
Yego's best attempt of 92.72 meters was the longest in the last 14 years in the javelin, as he added to this 2014 Commonwealth Games title.
Ihab Abdelrahman El Sayed also made history with Egypt's first medal in global competition, winning silver after an 88.99m throw, while Finland's Tero Pitkamaki (87.64m) took the bronze.
Yego now trains in Finland, but spent his formative years coaching himself in Nairobi with the help of online videos. He missed out on the bronze medal at the 2013 world championships in Moscow on the final throw, but was not be be denied a medal this time.
The 26-year-old ended up prone on his chest after heaving the javelin away -- his performance was the third best of all time, making him the favorite to win gold at the 2016 Rio Olympics.
Yego was delighted with his throw, and proud to have made it to the top of his discipline from such unusual circumstances.
"Very few athletes have done what I have done. There will not be another YouTube athlete coming through. I want to go back and watch my throw, it was almost perfect," he said Wednesday.
Kenya ended day five in China on top of the medals table with six golds -- three more than second-placed Great Britain -- but some of the gloss has been taken off that achievement with the news that two of its runners have been suspended following positive drugs tests.
Koki Manunga and Joyce Zakary gave positive samples on August 20 and 21 respectively, and were withdrawn from their women's 400 meters heats.
Hyvin Kiyeng Jepkemoi won Kenya's other gold Wednesday with a thrilling victory in the women's 3,000m steeplechase, finishing just ahead of Tunisia's Habiba Ghribi and Germany's Gesa Felicitas Krause.
Usain Bolt and Justin Gatlin will face off in another final
on Thursday after both won their men's 200m semis.
Bolt clocked 19.95 seconds -- over half a second outside the world record he set in the same stadium in winning gold at the 2008 Beijing Olympics.
"I'm trying to preserve as much as possible for the final. The 200m is my best event," said the Jamaican superstar, who edged Gatlin in Sunday's 100m to retain his title.
The American, the 2005 champion, was also impressive in running 19.87s.
In other finals contested Wednesday, South Africa's Wayne van Niekerk won a blistering 400m in 43.48 seconds -- the fourth best of all time.
He had to receive medical attention after his gold medal run, such was the effort he deployed to relegate LaShawn Merritt of the United States and Olympic champion Kirani James to the minor medals, with all three running under 44 seconds.
In the women's 400m hurdles, Czech Zuzana Hejnova defended her title from American duo Shamier Little and Cassandra Tate, while Cuba's Yarisley Silva cleared 4.90m to win the women's pole vault, having been bronze medalist in 2013.