Qatar's Ashraf Amgad Elseify in action in the hammer (Getty Images) © Copyright
It was an improvement of more than two metres on the previous World Junior record of 82.97m thrown by Spain's Javier Cienfuegos in 2009.
"I came here with the intention of throwing 83 metres and beating the record, I knew I could do that because I had been training well, but when I let go of my big throw in the fifth round I watched it in the sky and thought, 'it's going so, so far'. I was amazed even though I had been building up to a big throw with two throws over 81 metres in the two rounds before," said Elseify in fairly fluent English.
"Thinking now, I think I was physically ready to throw 85 metres even if I didn't quite believe before the competition that I would do it," he added, shortly after he was confirmed as the new champion.
In fact, he had already added almost a metre to his personal best with his third round throw of 81.84m and then followed it up with 81.60m.
Even his first two efforts of 77.23m and 78.61m would have sufficed for victory before he finished off his phenomenal series with a foul.
With Hungary's silver medallist Bence Pasztor back on 76.74m, Elseify had the largest winning margin ever in any throwing event, by either a man or a woman, in the history of the World Junior Championships.
Elseify's exhibition was coincidently watched very intently by Russia's Yuriy Sedykh, the man who still holds the senior World record for almost 26 years with the 86.74m he threw to win the 1986 European Athletics Championships.
Sedykh, now living in Paris, had come to Barcelona with his wife and Shot Put World record holder Natalya Lisovskaya to watch his daughter Alexia, who competes in the colours of France, take the silver medal in the women's event held earlier on Saturday night.
Showing off for Sedykh
However, Sedykh needed no encouragement to stay around and catch a first-hand look at the man that one day might succeed him as the best hammer thrower the world has ever produced.
"I knew Sedykh was in the crowd and although I have never spoken with him, I wanted to show him what I could do. It was an inspiration knowing that he was there. One day, of course, I want to throw as far as him.
"I threw 85 metres with the 5kg hammer when I was a youth, I've now thrown 85 metres with the 6kg junior hammer; however, I hope people don't expect me now to throw 85 metres with the senior hammer next year," joked Elseify, who still has another two years in the junior ranks.
He will be eligible to defend his title at 2014 World Junior Championships in Eugene, United States. At his current rate of progress, Elseify might be threatening the 90 metres line, or even throwing beyond it, by the time he arrives in the place fondly known among American athletics fans as 'Track Town'.
"However, firstly I want to go to Moscow for the World Championships there next summer. I want to fight with the seniors and also learn from them."
At just 17, Elseify has never thrown the 7.26kg Hammer in competition but it does make you wonder what he would be capable of with it in his hands.
The best distance on record by a junior is 78.33m by Finland's 1998 World Junior Championships gold medallist Olli-Pekka Karjalainen.
Elseify originally hails from Egypt and was talented spotted when he won the Egyptian youth title in Cairo as a 15 year-old. He was invited to train in Qatar, under the tutelage of Russian hammer coach Alexey Malikov.
At that point, it was an easy decision for Elseify to take up Qatari citizenship and he made his debut for his adopted country at the GCC (the six-member regional Gulf Cooperation Council) Championships in Mecca in April 2011 and he has never looked back.
"I am based at the Aspire Academy. In addition to my training, I am learning English and also teach it to younger students there," explained Elseify.
"Other than that, the main things I do are play basketball and speak to my mother at home in Egypt. Oh yes, and I watch videos of Primoz Kozmus, I really like his technique," added the Qatari youngster who might be battling head-to-head with the Slovenian 2008 Olympic Games champion in the near future.
Phil Minshull for the IAAF