Open to the eight best players under 21 on the senior circuit, the tournament boasted several innovations such as video cameras replacing human line judges and sets comprising four games.
There was also the chance for players to talk with their coaches during the breaks between sets and spectators were allowed to move along the sides during play.
Chung, 21, and 54th in the world rankings, rallied from a set down to see off his Russian opponent who is rated at number 37 following his run to the last eight at the US Open in September.
The South Korean, who beat Rublev in the round robin stages of the tournament, triumphed 3-4 4-3 4-2, 4-2 in just under two hours to claim his first major trophy.
"After losing the first set and down one break in the second, I was really nervous, really angry, but I tried to have a poker face," said Chung.
"I'm trying to create an image of being really strong mentally and I starting playing better and better," he said.
The former student of the Nick Bollettieri Tennis Academy in Florida, who has turned to a mind coach to help him deal with the pressure of tennis, received 335,000 euros for finishing the event undefeated.
Chung revealed that his training as to how to remain composed had helped him in Milan.
"The coach says all the time, first try to stay calm and in control, to have a chance to play better and better."
Rublev conceded he had been unnerved by Chung’s icy tenacity.
"I was playing much better than him,” said the 20-year-old. “I was dictating the match and everything changed because he was always there.
"He was always focused. He was always in the match.No matter if something goes wrong, he was still fighting. And me, from a little thing, I just lose my control and that's it. I just lost because of my head. Mentally he's really strong."
Momentum swung towards Chung in the third set as Rublev's frustration broke through over his inability to wear down his opponent who is the first South Korean to lift an ATP World Tour singles trophy since Lee Hyung-Taik won in 2003 at Sydney.
Medvedev took third place after Croatia's Borna Coric pulled out from their play-off due to injury.