By Dmitriy Rogovitskiy
MOSCOW (Reuters) - U.S. Open champion Marin Cilic was made to work hard before he earned a 6-3 3-6 6-3 win over 128th-ranked Russian journeyman Evgeny Donskoy to reach the quarter-finals of the Kremlin Cup on Wednesday.
Cilic was pushed to the limit at times but claimed victory in just under two hours to keep alive his hopes of qualifying for next month's ATP Tour Finals.
The Croatian second seed had the greater composure in the decider, breaking wildcard Donskoy three times while just about managing to keep his own serve functioning, despite being broken twice by the 24-year-old Russian.
"I am generally happy with today's match," said Cilic, who will next face either Tommy Robredo or Filip Krajinovic.
"In the first match of a tournament, I always feel a bit rusty.
"I was really surprised by my opponent. I had never played Donskoy before and had not even trained with him. He played a great game today."
The Croat currently stands sixth in the "Race to London" for the end-of-season ATP World Tour Finals which will feature the top eight players.
Novak Djokovic, Roger Federer, Rafa Nadal and Australian Open winner Stanislas Wawrinka have already qualified, while several players are still in contention to grab the four remaining places.
THE RACE TO LONDON:
1 Novak Djokovic 9010-qualified
2 Roger Federer 8020-qualified
3 Rafa Nadal 6745-qualified
4 Stan Wawrinka 4805-qualified
5 Kei Nishikori 4265
6 Marin Cilic 3990
7 Tomas Berdych 3945
8 Milos Raonic 3750
- - - - - - - - - - - -
9 David Ferrer 3715
10 Andy Murray 3655
11 Grigor Dimitrov 3450
(Reporting By Dmitriy Rogovitskiy, Editing by Neville Dalton)