Roger Federer returned to the summit of men’s tennis for the first time in more than five years and became the oldest world No 1 in the sport’s history after he proved too strong for Robin Haase at Rotterdam's ABN Amro World Tennis Tournament.
The 36-year-old Swiss great secured his spot in the history books and the last four of the tournament with a 4-6 6-1 6-1 victory against his Dutch opponent on Friday.
Federer, who needed to reach the semi-finals in order to overtake Rafael Nadal when the rankings are next updated on Monday, was last the top-ranked player in November 2012 and he has beaten the record of Andre Agassi, who was 33 when he topped the standings in 2003.
"Reaching No 1 is one of, if not the ultimate achievements in our sport," said Federer, who will next meet Andreas Seppi after the Italian prevailed 7-6(4) 4-6 6-3 against Daniil Medvedev.
"Sometimes at the beginning, you get there just because you play so well. Later, you sometimes try to fight it back and you wrest it back from somebody else who deserved to be there, and when you're older you feel like you have to put maybe double the work in. So this one maybe means the most to me throughout my career."
Haase, who had lost the pair's previous two meetings, started tentatively and faced three break points in his opening service game of the match, but he showed some encouraging resolve to fight them off and hold serve.
The first set remained on serve until the ninth game when the world No 42 fired a forehand winner to secure the first break of the match and the Dutch player consolidated the break with a composed service hold to secure the opener.
Federer, who claimed a record-extending 20th Grand Slam with a successful defence of his Australian Open title last month, responded impressively and grabbed a break in Haase's first service game of the second set, before a further break by the veteran forced a deciding set.
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.
Meanwhile, second seed Grigor Dimitrov booked his place in the last four with a 6-3 6-4 victory against Russia's Andrey Rublev.
The Bulgarian world No 4 will meet David Goffin in Saturday's semi-finals, the pair's first meeting since they met in the title match at the ATP Finals last year, after the Belgian benefited from a withdrawal by 2014 champion Tomas Berdych through illness.
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