Chung Hyeon has doused the fire of Russian top seed Andrey Rublev to win the inaugural Next Gen ATP Finals.
The South Korean was outplayed in the first set and was behind in the second before taking control to win 3-4 (5-7) 4-3 (7-2) 4-2 4-2.
The 21-year-old Chung went through the five-day round-robin tournament in Milan unbeaten and pocketed a $390,000 ($A510,000) cheque in the process.
A high-quality final full of sublime ball-striking was a fitting end to a promising debut for an event which has experimented with a range of innovations such as shorts sets, 'sudden-death' deuces and on-court coaching.
The 20-year-old Rublev, at 37th the highest-ranked qualifier for the event restricted to players aged 21 and under, lost his cool as the relentless Chung turned the match around.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
But the Muscovite showed tremendous resolve to survive a deciding point deuce, effectively match point, when serving at 1-3 in the fourth set, winning a ferocious baseline exchange.
The 54th-ranked Chung showed his first sign of nerves when he double-faulted at 30-30 in the next game but Rublev wasted the break point with a shanked forehand.
At deuce Rublev still had the chance to drag the set into a tiebreak but Chung struck a forehand winner to seal victory in just under two hours of compelling action.
"I can't believe I won my first title, I cannot believe it," Chung said.
"I played well all week but needed to play my best in the final."
Chung is the first South Korean to win an ATP singles trophy since 2003.
Rublev, who began his ATP Tour title collection in Umag this year, looked close to tears at the end but his performance, and that of Chung's, suggested both will be challenging for some of the biggest prizes in the sport before long.
The match for third place in the competition resulted in a walkover as Croatian Borna Coric withdrew before the contest, handing the win to Russian Daniil Medvedev.
In the likes of Canadian teenager Denis Shapovalov, a third Russian Karen Khachanov and American Jared Donaldson, the future looks bright for the men's Tour.
Whether or not any of the rule changes trialled this week ever become regular features remains to be seen, although the 25-second shot clock and shorter warm-ups were popular with players and fans alike.
