Caroline Wozniacki completed the New York City marathon in good time! How can an athlete who already spends most of her physical energy on tennis be able to muster up even more energy to fun a marathon? Caroline Wozniacki posted an Instagram photo to show what her secret was. And to snub her ex-fiance Rory McIlroy.

 My secret to finishing the marathon.... The carb loading the day before not one but 2 popcorns lol..

Foto kiriman Caroline Wozniacki (@carowozniacki) di Nov 11, 2014 at 3:33 PST

Turns out the world number 9’s secret is eating a lot of popcorns before the marathon!

Serena Williams, who accompanied Caroline in her popcorn eating endeavor, was there for the tennis player when she crossed the finish line in Central Park. Looks like the saying “sisters before misters” definitely applies to Caroline Wozniacki and Serena Williams!

The invincible Caro finished the marathon in three hours and 26 minutes.

"I never tried anything this hard," Wozniacki said according to New York Daily News. "This is the toughest physical challenge ever.

"You have to keep going, keep going. I just kept grinding out there.I know I can be out there for hours and be fine. I can keep battling it out there and I think that's a great mental advantage to have when you go out to play."

Congratulations to Caroline Wozniacki for completing the New York City Marathon! Rory McIlroy should really count his losses.