Milan - South Korean Hyeon Chung became the first player to book his ticket to the semi-finals of the Next Gen ATP Finals in Milan on Wednesday.
The 54th-ranked Chung made it two wins out of two in the round robin format being used in the inaugural edition of the under-21 version of the ATP Tour finals.
Chung beat Russia's Andrey Rublev 4-0, 4-1, 4-3 (7/1) on Wednesday in their Group A match a day after rallying from a set down to get past Canadian Denis Shapovalov.
"The score looks easy, but it was not easy on the court. Every point was a fight," said 21-year-old Chung who is guaranteed of finishing top of the group.
Pre-tournament favourite Rublev, ranked 37th and winner of his first title in Umag this year, had won his opener against Italian wildcard Gianluigi Quinzi.
Rublev can still make the semi-finals on Thursday when he plays Shapovalov.
The tournament has brought together eight emerging stars tipped as the Rafael Nadal, Andy Murray, Novak Djokovic and Roger Federers of the future.
Results from the second day of the Next Gen ATP finals under-21 tournament in Milan on Wednesday:
Denis Shapovalov (CAN) bt Gianluigi Quinzi 4-1, 4-1, 3-4 (5/7), 4-3 (7/5)
Hyeon Chung (KOR) bt Andrey Rublev (RUS) 4-0, 4-1, 4-3 (7/1)
Borna Coric (CRO) bt Daniil Medvedev (RUS) 4-3 (7/5), 2-4, 4-1, 4-2
Karen Khachanov (RUS) bt Jared Donaldson (USA) 4-1, 4-3 (7/3), 4-2
Group A (Won/lost) (Sets) (Games)
Hyeon Chung 2-0 6-1 25-15 - qualified
Denis Shapovalov 1-1 4-4 26-22
Andrey Rublev 1-1 3-5 17-26
Gianluigi Quinzi 0-2 3-6 23-28
Group B (Won/lost) (Sets) (Games)
Borna Coric 2-0 6-1 26-17
Daniil Medvedev 1-1 4-4 24-26
Karen Khachanov 1-1 4-3 24-20
Jared Donaldson 0-2 0-6 13-24
Note: Round robin format, best of five sets but first to four games in each set. Top two from each group progress to the semi-finals, with the final on Saturday.