Roger Federer became the oldest world No 1 after he beat Robin Haase in the World Tennis Tournament quarter-finals in Rotterdam.

The 36-year-old Swiss, who won his 20th grand slam title last month by claiming a sixth Australian Open, replaced Rafael Nadal at the top of the ATP rankings with a 4-6, 6-1, 6-1 victory over the Dutchman.

“Reaching No 1 is one of, if not the ultimate achievement in our sport,” Federer said afterwards. “Sometimes at the beginning you just kind of get there because you played so well but later you have to fight for it and have to wrestle it back from someone who deserves to be there. When you are older you maybe have to put double the work in. This maybe means the most to me in my career.”

Federer has surpassed Andre Agassi as the oldest player to occupy the summit of the men’s game – the American was 33 when he was last on top in September 2003. Agassi was among the first to congratulate Federer: “Roger Federer continues to raise the bar in our sport. Congratulations on yet another remarkable achievement!!” he said on Twitter.

Federer’s return to the top spot will be formally rubber-stamped when the men’s tour rankings are published on Monday.

Federer also beats the mark set by the record holder in the women’s game, Agassi’s compatriot Serena Williams, who was 35 when she was last No 1 in May 2017.