Roger Federer will not only become the oldest man to reach world number one on Monday, but his latest ascent to the top will mark the longest gap between stints at the summit.
"It was extremely complicated tonight", said Federer, who recorded 11 aces and no double-faults.
The last time Federer reached the pinnacle of tennisdom was in 2012.
The final set saw Federer continue his dominance and three further breaks of serve helped the two-time Rotterdam champion over the winning line against a tiring Haase. He now leads Kohlschreiber 13-0 and has won both career meetings against Haase.
"This is an exciting challenge, I've struggled to try and get there".
Also, Grigor Dimitrov won by a almost identical score as Federer, defeating Filip Krajinovic 7-6 (4), 7-5. "It was quite a relief at the end".
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Here are some facts about Federer and his ranking.
The 36-year-old Swiss, who won his 20th grand slam last month by claiming a sixth Australian Open title, replaced Rafael Nadal at the top of the ATP rankings with a 4-6, 6-1, 6-1 victory over the Dutchman. I guess you don't want to give myself too much time. "I had to win a lot of matches", he said. I would have had great regret if I had not come here this week.
Dimitrov will meet Andrey Rublev in the quarters after the Russian got the better of Damir Dzumhur 6-4 7-6 (7-4), while Daniil Medvedev came from a set down to defeat Pierre-Hugues Herbert 3-6 7-6 (7-2) 6-4 to set up a clash with Andreas Seppi.
Now only the Netherlands' Robin Haase, a 6-4, 6-0 victor late Thursday night over Dutch wildcard Tallon Griekspoor, stands in his way.
The victor of their tie will meet either Andreas Seppi or Daniil Medvedev, while Tomas Berdych, David Goffin, Andrey Rublev and Grigor Dimitrov occupy the other half of the draw.
Rounding out the quarterfinal field, Belgium's David Goffin and Tomas Berdych of the Czech Republic, the event's No. 4 and 6 seeds, respectively, will face each other.