South Korea’s Chung Hyeon has maintained his 100 per cent record at the Next Gen ATP Finals with a crushing victory over Russian Andrey Rublev to surge ahead in Group A.

The 21-year-old is showing a liking for the rule innovations being tested in Milan and proved too solid for Rublev, the highest ranked player in the ATP’s new showcase event for the best players aged 21 and under.

The world No.54, easy to spot in his distinctive white spectacles, won 4-0 4-1 4-3(1) to follow up his defeat on Tuesday of Canadian Denis Shapovalov – sealing a semi-final spot with a round-robin match to spare.

Chung finished off Rublev in just over an hour, slightly longer than it took Karen Khachanov to beat American Jared Donaldson 4-1 4-3(2) 4-2 in Group B.

Donaldson is still without a set after two matches.

“I’m so happy to get my second win here, I had never played Rublev before,” Chung said.

“I’ve never played with these rules before but I like them.”

Shapovalov notched his first win when he beat Italian wildcard Gianluigi Quinzi 4-1 4-1 3-4(5) 4-3(5).

The 18-year-old raced through the opening two sets against his fellow former junior Wimbledon champion before the match burst into life when the Italian found another gear.

Despite double-faulting on match point, however, Shapovalov claimed victory and will need to beat Rublev to reach the semis.

The eight-man tournament, showcasing the players tipped to be the future of men’s tennis, is using radical new rules aimed at increasing the popularity of the sport.

As well as sets being played only to four games, there are no advantage points, shot clocks to enforce the 25-second between points rule, no let serves and coaching via headphones at the end of sets.

Line judges have also been removed for the tournament with Hawk-Eye technology calling lines using an automated voice.