Most people celebrate their 40th birthday with a slap-up meal or a surprise party.
Gael Monfils, the maverick Frenchman who always knows how to have fun on the court, marked his milestone by winning a Grand Slam match at the US Open.
Playing in the final major of his career, Monfils ensured he had a unforgettable night with a 2-6 6-1 6-2 6-0 victory over Paraguayan opponent Adolfo Daniel Vallejo.
The former world number six is the oldest man to win a US Open main-draw match since Jimmy Connors - who also won on his 40th birthday in 1992.
The New York crowd made the occasion even more memorable for Monfils by bursting into an impromptu rendition of Happy Birthday during his post-victory interview.
"To play on my 40th birthday is very special," said the 2016 US Open semi-finalist, who announced last year he will retire at the end of this season.
"The atmosphere [in New York] is always electric - I feel great here. I always try to play great tennis and put on a great show."
Addressing the thousands of fans who created a celebratory atmosphere on Louis Armstrong Stadium, he added: "You guys rock - let's keep it up for the second round."
Playing in his 18th and final US Open, Monfils made a nervous start against 60th-ranked Vallejo.
However, he quickly settled into the match and dominated the next three sets to secure a 131st Grand Slam match win - extending his all-time record for a Frenchman.
It was a typically entertaining display from the charismatic Monfils, who enthralled the crowd with the stylish shot-making and athleticism for which he is known.
"I didn't want to lose first round, that's for sure," said Monfils, who revealed he was given a watch by his wife Elina Svitolina - the two-time Wimbledon semi-finalist - as a birthday present.
"Somehow I felt like even with a sloppy start, I could do better. I kept going for my shots, being versatile with my backhand, tried to use my forehand.
"My rhythm was there and then I had this feeling where I can be in cruise control."
Monfils will continue his farewell appearance at Flushing Meadows against American 14th seed Learner Tien.
One man also left celebrating in the early hours of the New York morning was top seed Alexander Zverev.
The 29-year-old German survived a huge scare against Italy's Lorenzo Sonego to win a five-set thriller at almost 2am on Arthur Ashe Stadium.
Zverev is aiming to reach the final for the third successive Grand Slam, but almost fell at the first hurdle after being pushed to the limit by 89th-ranked Sonego for almost five hours.
Sonego, 31, produced a stunning performance to lead by two sets to one - and was two points away from victory in the fourth set.
But Zverev, who won the first major of his career at the French Open before reaching the Wimbledon final, showed great resolve to escape with a 6-4 3-6 6-7 (7-9) 7-5 6-4 victory.
"I'm just happy I won - that's it," said Zverev.
"It was an incredible battle with ups and downs. I think it's the longest first round match I've ever played in my life.
"He played amazing tennis and would have beaten a lot of players for sure."
