Rotterdam - Second seed Grigor Dimitrov outlasted Serbia's Filip Krajinovic 7-6 (7/4), 7-5 to reach the Rotterdam Open quarter-finals on Thursday as Roger Federer waited to take another step closer to becoming the oldest world number one.

Dimitrov has now reached a second straight quarter-final in the Dutch city, advancing with 13 aces and saving all four break points he faced.

The Bulgarian will face Andrey Rublev on Friday after the 20-year-old Russian struggled for nearly two hours before finally seeing off Damir Dzumhur 6-4, 7-6 (7/4).

Rublev, the world number 34, forced his Bosnian opponent to save 10 of 15 break points while he saved nine of 13.

Russian Daniil Medvedev joined his compatriot in the last eight by beating Pierre-Hugues Herbert of France 3-6, 7-6 (7/2), 6-4.

The two-and-a-quarter-hour contest featured 13 aces from the loser and just four from the winner.

Thursday evening's highlight will feature Federer hoping to take the penultimate step towards regaining the number one ranking, becoming the oldest man by three years to own the honour.

The 36-year-old Swiss, with a record 20 Grand Slam titles, will face off against German Philipp Kohlschreiber, whom he has beaten in all of their previous 12 matches.