<p class="title">Roger Federer can become the oldest world number one today, a remarkable achievement for the 20-time Grand Slam title winner who admitted he "never imagined" hed get the opportunity.</p>.<p class="bodytext">The 36-year-old faces Dutchman Robin Haase in the quarter-finals of the Rotterdam Open where victory will allow him to replace old rival and close friend Rafael Nadal at the top of the rankings.</p>.<p class="bodytext">The Swiss would surpass Andre Agassi, who held the top spot in 2003 aged 33 years and 131 days.</p>.<p class="bodytext">It would be Federer's first time back at the summit since October 2012 having first claimed the top spot in February 2004.</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 as low as 17 in the world in January last year before he returned to form with the Australian Open title.</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 tomorrows match, I can't wait for it to come around."</p>.<p class="bodytext">Federer moved into the quarter-finals on Thursday with a hard-fought 7-6 (10/8), 7-5 victory over Germanys Philipp Kohlschreiber.</p>.<p class="bodytext">"Tonight was complicated, I had to fight and struggle," said Federer who has won three of the last five majors.</p>.<p class="bodytext">"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">Thursdays win was Federer's 13th in as many meetings against Kohlschreiber.</p>.<p class="bodytext">Second seed Grigor Dimitrov outlasted Serbia's Filip Krajinovic 7-6 (7/4), 7-5 to also reach the quarter-finals.</p>.<p class="bodytext">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.</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 can become the oldest world number one today, a remarkable achievement for the 20-time Grand Slam title winner who admitted he "never imagined" hed get the opportunity.</p>.<p class="bodytext">The 36-year-old faces Dutchman Robin Haase in the quarter-finals of the Rotterdam Open where victory will allow him to replace old rival and close friend Rafael Nadal at the top of the rankings.</p>.<p class="bodytext">The Swiss would surpass Andre Agassi, who held the top spot in 2003 aged 33 years and 131 days.</p>.<p class="bodytext">It would be Federer's first time back at the summit since October 2012 having first claimed the top spot in February 2004.</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 as low as 17 in the world in January last year before he returned to form with the Australian Open title.</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 tomorrows match, I can't wait for it to come around."</p>.<p class="bodytext">Federer moved into the quarter-finals on Thursday with a hard-fought 7-6 (10/8), 7-5 victory over Germanys Philipp Kohlschreiber.</p>.<p class="bodytext">"Tonight was complicated, I had to fight and struggle," said Federer who has won three of the last five majors.</p>.<p class="bodytext">"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">Thursdays win was Federer's 13th in as many meetings against Kohlschreiber.</p>.<p class="bodytext">Second seed Grigor Dimitrov outlasted Serbia's Filip Krajinovic 7-6 (7/4), 7-5 to also reach the quarter-finals.</p>.<p class="bodytext">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.</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>