WATCH | Roger Federer beats Philipp Kohlschreiber, just one win away from becoming World No. 1

Roger Federer is one win from becoming the oldest world number one in ATP Tour history after beating Philipp Kohlschreiber 7-6(8) 7-5 in the last 16 of the Rotterdam Open on Thursday.

The 36-year-old needs to reach the semi-finals to overtake Rafael Nadal at the top of the rankings and reclaim the world number one ranking for the first time since November 2012.

Evergreen Federer, the 20-times grand slam champion, faces local favourite Robin Haase in the last eight on Friday.

Kohlschreiber, 34, had not beaten Federer in 12 attempts but on his own service game proved a tough opponent for the Swiss, pushing him all the way to a first set tie-break.

The German even had two set points but could not convert them as Federer rallied and placed a forehand perfectly beyond Kohlschreiber to take the lead in the match after 54 minutes.

The second set followed a similar pattern but with Kohlschreiber, ranked 36 in the world, more attuned to Federer's serve and improving his return rate.

He still had to save four break points without getting close himself to threatening the Australian Open champion's serve.

Kohlschreiber's resistance was finally breached in the 11th game as Federer overpowered his opponent and went on to comfortably serve out the set.

Federer would surpass American Andre Agassi as the oldest world number one if he wins his next match in Rotterdam and he would also set another record of the longest gap (five years and 106 days) between periods as number one.

He already holds the record for most weeks spent at number one, having topped the rankings for a combined 302 weeks.