Hyeon Chung books semifinal place at Next Gen ATP Finals

Hyeon Chung remains undefeated after two matches at the Next Gen ATP Finals in Milan. MARCO BERTORELLO/AFP/Getty Images

South Korea's Hyeon Chung has booked his spot in the semifinals of the Next Gen ATP Finals in Milan after beating top seed Andrey Rublev in straight sets.

Chung, who won against Canada's Denis Shapovalov on Tuesday, took 68 minutes to beat Rublev 4-0, 4-1, 4-3 (1).

The Next Gen event -- which features eight players under the age of 21 -- is trialing a number of new rules including first-to-four sets and shot clocks.

Shapovalov got his first win of the tournament on Wednesday when he beat wildcard Gianluigi Quinzi 4-1, 4-1, 3-4 (5), 4-3 (5).

Second seed Karen Khachanov also recorded his first win with a straight sets victory over American Jared Donaldson.

In Wednesday's late match, Borna Coric joined Chung in the semifinals with his second win in as many days.

The Croatian beat Daniil Medvedev 4-3 (5), 2-4, 4-1, 4-2 in an hour and 34 minutes.