Russian number one Rublev, the highest-ranked qualifier for the tournament at 37th in the world, dominated his fellow 20-year-old with superior firepower to win 4-1 4-3(6) 4-1 in little over an hour at the Fiera Milano.
Chung, ranked 54, followed Rublev into the final when he dispatched Russian, Daniil Medvedev, 4-1 4-1 3-4(4) 1-4 4-0.
It was too easy for Chung in the opening two sets but 65th-ranked Medvedev emerged from his slumber to make a match of it.
Chung re-asserted his authority in the third set, although he did have to save three break points when leading 2-0 -- letting out a huge roar as he made his way back to his seat.
He then broke again to finish the job.
Coric, who perhaps regretted battling back from two sets down to win his final round-robin match against Karen Khachanov despite already having qualified, looked jaded and took his frustration out on his racket.
Twice he broke frames in the third set as Rublev raced away to victory and a final against either Chung Hyeon or fellow Russian Daniil Medvedev who are in action later.
Coric was too passive in the first set but revived in the second after coach Christian Schneider told his player, through headphones, to "give me more energy".
The Croatian got himself into a tiebreak but a poor forehand at 6-6 gave Rublev a second set point and he made no mistake.
One of the many innovations at the Next Gen Finals, the headphone exchanges between coach and player make for interesting listening for the crowd and TV audiences and Coric's reaction to losing the second set was candid.
"I don't know what to do any more," he said, before crumbling to defeat.
Coric even became irate with one live Hawkeye call -- the system that has replaced human line judges at the event.
Rublev, who came into the tournament on the back of three straight defeats, said it was his best performance so far and hopes to reverse his crushing round-robin loss to Chung.
"We'll see if I can change something," he told reporters. "The first match here, I wasn't playing that aggressive. I didn't play that good. I was missing a lot.
"So I hope tomorrow I can show a better game."
(Reporting by Martyn Herman; Editing by Christian Radnedge)
