Roger Federer guaranteed himself a place in Tennis history with victory in Rotterdam on Friday.
The evergreen Swiss became the oldest world number one in the history of the sport after defeating Robin Haase to advance through to the semi-final of the World Tennis Tournament in the Dutch city.
Federer overcame an early scare to claim a 4-6 6-1 6-1 victory over Dutchman Hasse and thereby replaced Rafael Nadal at the top of the ATP world rankings.
At 36 years and 195 days old, Federer has also surpassed another icon of the sport.
American Andre Agassi was the previous holder of the record.
He was 33-years-old when he was on top of the world rankings back in September 2003 - an impressive feat that many thought would never be beaten.
And although it was Agassi who Federer replaced, the American was amongst the first to send him a congratulatory message on Twitter.
Agassi posted: "36 years 195 days...
"@RogerFederer continues to raise the bar in our sport. Congratulations on yet another remarkable achievement!!"
A classy reaction, although you'll have to look pretty hard to find someone who doesn't think Federer deserves the acclaim.
The 36-year-old won his 20th Grand Slam when he claimed another Australian Open Championship in Melbourne last month and that back up a stellar 2017.
The Aussie Open and Wimbledon were just two of his major achievements during a year when rivals Andy Murray and Novak Djokovic struggled with injury.
Federer's place at the top of the order will be formally rubber-stamped on Monday morning, when the Men's ATP Tour Rankings are published on Monday morning.
Federer also topped the landmark set by Agassi's female compatriot, Serena Williams, who was 35-years-old when she was world number one in the women's game back in May last year.
And there's little sign of him slowing down anytime soon.
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