The Swiss is now the oldest male number one since Andre Agassi and he will strengthen his grip on the summit of the men’s game if he is to claim his third title in Rotterdam on Sunday.
'Dream come true'
“Reaching number one is one of, if not the ultimate achievement in our sport,” grinned Federer courtside.
“When you’re older you maybe feel you have to put double the work in so this one maybe means the most to me throughout my career.
“At nearly 37-years-old it is a dream come true and I honestly cannot believe it.”
The pre-tournament focus rested upon the Swiss and his surprise decision to accept a wild card into the ATP 500 tournament after a successful two weeks in Melbourne in which he captured his 20th Grand Slam title.
He dismissed Ruben Bemelmans and Philipp Kohlschreiber without too much of a fuss earlier this week but he surrendered the opening set for the first time in 2018 against the laser-sharp Haase.
The Dutchman, who has been battling a fever this week, punished a weak serving exhibition from Federer in the first set and broke the Swiss in the ninth game of the match.
He served out the set in 34 minutes as Federer’s first serve percentage stood at 42. As so often with the 36-year-old, however, he sharpened his focus to begin set two.
Breaking Haase to love, Federer confirmed the double break of serve for a 5-1 advantage when the Dutchman sent a forehand long.
He relinquished only nine points in the second set and, with Haase visibly struggling, Federer took control of the deciding set.
Covering the court with an exuberance that belies his years, he broke the resolve of the Dutchman before he was able to digest a disappointing second set.
A mesmerizing backhand pass saw Federer race out to a 4-0 lead and from there would be no looking back.
He may rue the bittersweet fashion in which he sealed victory after a Haase double-fault on set point, but this evening will live long in the memory of the 36-year-old.
Age, after all, is only a number.