<p class="title">Roger Federer moved to within one victory of becoming the oldest man to take the world number one ranking on Thursday with a hard-fought 7-6 (10/8), 7-5 victory over Germany's Philipp Kohlschreiber at the Rotterdam Open.</p>.<p class="bodytext">The 36-year-old will now face Robin Haase in the quarterfinals on Friday.</p>.<p class="bodytext">"Tonight was complicated, I had to fight and struggle," said Federer. "I had a good game plan going in, but I was never able to completely pull it off.</p>.<p class="bodytext">"He came out with a clean start. I was serving well, that's a great sign. I'd rather do that and return poorly."</p>.<p class="bodytext">Thursday's win was Federer's 13th in as many meetings against Kohlschreiber.</p>.<p class="bodytext">The first set was a 54-minute struggle with the top seed having to work hard against the veteran German who was broken for the only time in the match when he double-faulted to hand Federer a 6-5 lead in the second set.</p>.<p class="bodytext">Federer, the 20-time Grand Slam title winner, then eased to victory in the 12th game with a volley winner on second match point.</p>.<p class="bodytext">The Swiss is excited about the possibility of returning to the top of the rankings 19 years after he played Rotterdam in 1999 on his first career wild card.</p>.<p class="bodytext">"This is an exciting challenge, I've struggled to try and get there. I had to win a lot of matches last year," said Federer, who was world number one for the first time in February 2004.</p>.<p class="bodytext">However, he was last at the summit in October 2012 and slumped to 17 in the world in January last year.</p>.<p class="bodytext">"I never imagined this after my (February 2016) knee surgery. Number one is a tough place to get to.</p>.<p class="bodytext">"The most important thing is to be healthy, I would have had great regrets if I had not come here this week. I'm very excited for tomorrow's match, I can't wait for it to come around."</p>.<p class="bodytext">Second seed Grigor Dimitrov outlasted Serbia's Filip Krajinovic 7-6 (7/4), 7-5 to also reach the quarterfinals.</p>.<p class="bodytext">Dimitrov has now reached a second straight quarterfinal in the Dutch city, advancing with 13 aces and saving all four break points he faced.</p>.<p class="bodytext">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).</p>.<p class="bodytext">Rublev, the world number 34, forced his Bosnian opponent to save 10 of 15 break points while he saved nine of 13.</p>.<p class="bodytext">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.</p>.<p class="bodytext">The two-and-a-quarter-hour contest featured 13 aces from the loser and just four from the winner.</p>
<p class="title">Roger Federer moved to within one victory of becoming the oldest man to take the world number one ranking on Thursday with a hard-fought 7-6 (10/8), 7-5 victory over Germany's Philipp Kohlschreiber at the Rotterdam Open.</p>.<p class="bodytext">The 36-year-old will now face Robin Haase in the quarterfinals on Friday.</p>.<p class="bodytext">"Tonight was complicated, I had to fight and struggle," said Federer. "I had a good game plan going in, but I was never able to completely pull it off.</p>.<p class="bodytext">"He came out with a clean start. I was serving well, that's a great sign. I'd rather do that and return poorly."</p>.<p class="bodytext">Thursday's win was Federer's 13th in as many meetings against Kohlschreiber.</p>.<p class="bodytext">The first set was a 54-minute struggle with the top seed having to work hard against the veteran German who was broken for the only time in the match when he double-faulted to hand Federer a 6-5 lead in the second set.</p>.<p class="bodytext">Federer, the 20-time Grand Slam title winner, then eased to victory in the 12th game with a volley winner on second match point.</p>.<p class="bodytext">The Swiss is excited about the possibility of returning to the top of the rankings 19 years after he played Rotterdam in 1999 on his first career wild card.</p>.<p class="bodytext">"This is an exciting challenge, I've struggled to try and get there. I had to win a lot of matches last year," said Federer, who was world number one for the first time in February 2004.</p>.<p class="bodytext">However, he was last at the summit in October 2012 and slumped to 17 in the world in January last year.</p>.<p class="bodytext">"I never imagined this after my (February 2016) knee surgery. Number one is a tough place to get to.</p>.<p class="bodytext">"The most important thing is to be healthy, I would have had great regrets if I had not come here this week. I'm very excited for tomorrow's match, I can't wait for it to come around."</p>.<p class="bodytext">Second seed Grigor Dimitrov outlasted Serbia's Filip Krajinovic 7-6 (7/4), 7-5 to also reach the quarterfinals.</p>.<p class="bodytext">Dimitrov has now reached a second straight quarterfinal in the Dutch city, advancing with 13 aces and saving all four break points he faced.</p>.<p class="bodytext">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).</p>.<p class="bodytext">Rublev, the world number 34, forced his Bosnian opponent to save 10 of 15 break points while he saved nine of 13.</p>.<p class="bodytext">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.</p>.<p class="bodytext">The two-and-a-quarter-hour contest featured 13 aces from the loser and just four from the winner.</p>