Foes on the court. Friends everywhere else. Serena Williams and Caroline Wozniacki celebrated their 2014 US Open final, which Williams won, by partying in New York on Sunday night.

And the tennis stars recently explained their deep friendship, proving that sometimes your competition can also be your greatest ally.

''Serena is a fun girl. She's so nice to hang out with. Always makes me laugh and makes everyone around her laugh,'' Wozniacki told the Boston Globe. ''Definitely a very inspiring person to be around.''

Wozniacki's admiration of Williams was clear when the 24-year-old Danish tennis player lost to 33-year-old Williams in two sets (6-3, 6-3) during the US Open Women's final on Sunday.

"You're an unbelievable friend," said Wozniacki, addressing her pal in a post-match interview, "and you definitely owe drinks later."

The ladies did indeed have drinks. Williams, who masterfully earned her 18^th Grand Slam title at the Open, shared pictures on Instagram of she and Caroline out on the town later that evening.

The two even caught up with Joe Jonas, who also tweeted a photo with the tennis stars.

Williams and Wozniacki have been close for some time, although neither let their bond get in the way of their latest Grand Slam match.

''The friendship, while we are on court, is put aside. We are both competitors," said Wozniacki before the Open final, according to the Boston Globe. "After the match, one of us is going to congratulate the other and we're going to be friends again. It's fine.''

Though friends for years, the pair's camaraderie reportedly grew after Williams helped Wozniacki through the breakup of her engagement to golf star Rory Mcilroy.

"Obviously, lately, we've gotten a lot closer," Williams told the New York Times in an interview.

"Serena is one of my best friends," Wozniacki also revealed to the publication. "For a long time. But especially in the last year.

"Sometimes things happen in life and you kind of need a friend, and she stepped up and was there for me," Wozniacki added.

And the fierce duo definitely supported each other during the last week of the 2014 Open. The two even attended a New York Knicks basketball game just before their match, leaving all thoughts of tennis on the hardcourt.