They go to the beach together and they celebrate at NBA playoff games together. They dress up together and they dine out together.
On the court, they play against each other, but until now, Serena Williams and Caroline Wozniacki have never faced off in the final of a Grand Slam tournament.
That will happen Sunday at the U.S. Open. In the semifinals Friday, Williams, the top seed, ran over 17th-seeded Ekaterina Makarova 6-1, 6-3. Wozniacki, the No. 10 seed, defeated unseeded Shuai Peng 7-6, 4-3 (retired).
"I definitely believe that no matter who stands on the other side of the net I can win the match," Wozniacki says. "The last two times I played Serena, we played really two tough three-set matches. You know, it's going to be the U.S. Open finals. It's going to be a tough one. It's going to be exciting."
If anyone is suited for facing a close friend in a championship match, it's Williams. She went against sister Venus in eight of her 21 Grand Slam singles finals.
"If I can play Venus, I can play anybody. I grew up with Venus," Williams says. "We actually lived together going on 33 years, which is kind of sad."
Wozniacki, who is nearly eight years younger than Williams, rose to stardom when she reached the U.S. Open final in 2009 and earned the world No. 1 ranking in 2010. Williams was cordial with Wozniacki on the court and during WTA-related events during this time, but it was through a strange incident that their friendship became more evident.
During an exhibition in Brazil versus Maria Sharapova in December 2012, Wozniacki stuffed her bra and shorts to imitate Williams while also trying to copy Serena's grunt.
Some suggested the stunt had a racist meaning. Williams waited weeks to respond to such allegations until she told the USA Today's Douglas Robson in an email:
"I know Caro and I would call her my friend and I don't think she (meant) anything racist by it."
However, Williams also said: "I must add if people feel this way she should take reason and do something different next time." According to the article, a smiley emoticon was added after that sentence in the email.
Robson's article acknowledged Williams and Wozniacki had somewhat of a developing friendship at the time. Wozniacki visited Williams after her 2011 surgery for a hematoma in her stomach, and the two "traded advice on everything from jewelry to boyfriends."
The two continued to build on that relationship, and in May when Wozniacki's fiancé, Rory McIlroy, called off their engagement shortly after sending out wedding invitations, Williams provided public support. Wozniacki, who had been dating the golf superstar since 2011, received an outpouring of messages in the aftermath of her break-up. She only responded to one.
Just days later, Wozniacki arrived in South Florida for a flamboyant week with Williams. Paparazzi found the duo dining and partying in Miami. Pictures were snapped of the ladies on the beach, but perhaps the most popular photos came from American Airlines Arena. Williams and Wozniacki attended Miami's Game 6 conference-championship clincher and celebrated on the court with the Heat.
— Caroline Wozniacki (@CaroWozniacki) May 31, 2014
So what if it is Greg Oden?
From a paparazzi sense, Williams was the pick-me-up Wozniacki got after breaking up with McIlroy. The 17-time Grand Slam champion showed Caro a Miami party. And it had nothing to do with tennis.
"We never talk tennis so much since we spend so much of our life on the court," Williams says. "Same with me and Venus. The last thing on our minds is tennis. If anything, it's to not think about a forehand or a backhand."
Wozniacki says, "Serena is a fun girl. She's so nice to hang out with. She always makes me laugh and makes everyone around her laugh. Definitely a very inspiring person to be around."
Although they may talk more about LeBron James' jump shot or the latest music in Miami clubs than tennis, Williams and Wozniacki did discuss the U.S. Open draw when the brackets were released.
"We were saying when the tournament started, we're like, 'Yes, we're in separate sides of the drawing, so hopefully we can meet in the finals,'" says Wozniacki, whose only Grand Slam final was a straight-set loss to Kim Clijsters at Flushing Meadows
Wozniacki certainly wants to get a piece of her friend Serena. The players met in both Montreal and Cincinnati in August. Williams took both matches in three sets after Wozniacki won the first set. Overall, Williams is 8-1 in their meetings, including wins over Wozniacki in the 2011 U.S. Open and 2012 Olympics.
While Williams saw Wozniacki on the other side of the draw, Serena was more focused on another potential opponent she knows well: Her sister.
"I would have loved to have seen Venus there. That goes unsaid," Williams says. "We (her and Wozniacki) played each other a lot recently in like the semis, I think, maybe the quarters once. So it was like, oh, it would be much better to play each other in the final than earlier on."
On paper, Williams and Wozniacki have both had difficult years at Grand Slams. Williams lost in the fourth round at the Australian Open, the second round at the French Open and the third round at Wimbledon. She has three titles this year and maintains the world No. 1 ranking, but she has not succeeded on the platform she has in the past. Wozniacki did not fare any better at the first three grand slams, losing in the third, first and fourth rounds (in chronological order). Wozniacki also had not made a Grand Slam semifinal since the 2011 U.S. Open before this year's tournament.
"Of course we were like, that would be great if we could see each other in the final, because we both hadn't had the greatest Grand Slam year," Williams says.
As friends, the Williams and Wozniacki have their eyes on another New York event. Wozniacki will return in November, as she plans to run in the annual New York City marathon. Although Wozniacki has been under a bit of fire for pushing her body through marathon training, it has apparently not affected her game.
"I think she'll do great," Williams says. "She's been running and training for it. She's doing it for a charity. I think it's such a positive thing to do."
The 2014 season has been a marathon for both players. Both have been grinding all year to reach a grand slam final. On Sunday, they will take the court against each other, as friends and foes, for the big show.
This will be a final sprint. And neither will be rooting for the other. For now.
-- Follow Jeffrey Eisenband on Twitter @JeffEisenband.