Chung stays focused for third win, Rublev reaches semis

MILAN, Nov 9 (Reuters) - South Korea's Chung Hyeon topped Group A in the Next Gen ATP Finals with his third straight victory on Thursday and was joined in the last four by Russia's Andrey Rublev who ended the hopes of Canadian teenager Denis Shapovalov.

Chung was pushed hard by Italian qualifier Gianluigi Quinzi before winning 1-4 4-1 4-2 3-4(6) 4-3(3) in the first match to go past two hours at the inaugural event showcasing the world's best players aged 21 and under plus a batch of new rules.

Rublev, at 37th the highest-ranked player in the tournament, looked in trouble against Canadian teenager Denis Shapovalov in the evening session when he needed treatment on blisters.

But the rugged 20-year-old edged home in a deciding set tiebreak, winning 4-1 3-4(8) 4-3(2) 0-4 4-3(3) to take runners-up spot in Group A in another match that went past two hours.

Another Russian, Daniil Medvedev, fared better as the world number 65 beat American Jared Donaldson 3-4(3) 4-2 4-3(1) 4-0 for his second victory in Group B.

He was left sweating on hopes of a victory by Croatia's Borna Coric against Russian Karen Khachanov later on Thursday to guarantee a place in Friday's semi-finals.

Chung offered a new twist to the debate about shot-clock, one of several innovations being tested including short sets played to four games and no advantage points.

The 21-year old is a big fan of the scoreboard ticking down for the 25-second rule between points -- saying it meant he knew exactly how long he had to clean his distinctive white-framed spectacles.

In the past he has incurred the wrath of the chair umpire by going over time, but avoided that fate on Thursday in a match that lasted two hours and six minutes.

"I like shot clock, because sometimes I get a warning because I have to clean my glasses," said Chung, who has worn prescription sports glasses throughout his career and only took up tennis to improve his eyesight.

"I get the warnings all the time in long matches. So I like the shot clock."

All eight group matches before Chung's afternoon clash with Quinzi had been completed in less than two hours - averaging one hour 26 minutes as the ATP experiments with speeding up play. (Reporting by Martyn Herman, editing by Ed Osmond and Ken Ferris)