ROTTERDAM, Netherlands -- Roger Federer is within touching distance of becoming the oldest male to reach the top of the world rankings after marching into the quarterfinals of the ABN AMRO tournament.
The 20-time Grand Slam champion went through after making it 13 wins in as many matches against Philipp Kohlschreiber with a 7-6 (10-8), 7-5 triumph against his German opponent on Thursday.
One more victory at the indoor tournament in Rotterdam will ensure that Federer, 36, leapfrogs his old rival Rafael Nadal at the top of the world rankings.
Federer would also then become the oldest No. 1 male player, surpassing Andre Agassi, who holds the record at 33 years and 133 days.
"It was extremely complicated tonight," Federer said. "I couldn't find my range or rhythm. I think Philipp did that to me. It was a struggle.
"Today when the score was close I couldn't release my shots, so it was quite a battle. It was quite a relief at the end."
Federer, the 2005 and 2012 ABN AMRO champion, next meets home favorite Robin Haase, who beat compatriot Tallon Griekspoor 6-4, 6-0.
Grigor Dimitrov, Andreas Seppi, David Goffin, Tomas Berdych, Daniil Medvedev and Andrey Rublev also reached the quarterfinals.