Star-watching isn't anything new in the Big Apple, but some sports fans might have done a double take Wednesday in Central Park.

Roger Federer, one of the biggest sports stars on the planet, decided to drop in on one of the park's public tennis courts for a little practice ahead of his second-round US Open match against Mikhail Youzhny on Thursday.

"Central Park hitting ... Extremely cool experience," Federer posted on his official Twitter feed.

Federer later tweeted more photos of his practice session at the park.

When in Central Park 🎾🤹‍♂ pic.twitter.com/JOiFYETPqy — Roger Federer (@rogerfederer) August 31, 2017

Federer had to overcome an early deficit Tuesday night to edge 19-year-old American Frances Tiafoe 4-6, 6-2, 6-1, 1-6, 6-4. He dropped two more sets in the first-round match than he did the entire fortnight en route to his Wimbledon title.

The No. 3-seeded Federer, whose most recent of five championships at Flushing Meadows came in 2008, played with the roof closed at Arthur Ashe Stadium for the first time.

He missed last year's tournament, when the retractable roof made its debut, because he took off the second half of 2016 to let his surgically repaired left knee and a bad back fully heal.

"It felt like people were happy to see me again," Federer said.

Information from The Associated Press was used in this report.