One of the most important tennis matches I played last year wasn’t on television. There were no fans watching, except a few dogs laying in the grass. It was at Roxbury Park in Beverly Hills on a lazy afternoon in November. My opponent was my friend Tony Parker. The Spurs were in town playing the Lakers and Tony asked if we could go to the park to work on his game.

I hit a high lob over Tony’s head and he went running to the back line and returned it quite well, so I hit a drop shot right over the net. Tony had no chance, but luckily he had a teammate to rely on. Even before I hit the ball, Tony recognized what was happening and yelled, “Bobo, go to the net!”

Bobo is Boris Diaw, Tony’s teammate on the Spurs. Tony enlisted his help as his doubles partner against me. It was only fair. It was funny to see them communicate with one another like they were running plays on the court. It sounded like a foreign language to me. The scene must have looked ridiculous to people walking through the park. This one woman playing against two super tall guys who were yelling instructions to one another, but it took a long time for anybody to recognize us. Tennis felt really fun again — like it does when you’re a kid playing in the park.

I really needed that game.

That fall, I was in the middle of a very tough time in my life. A foot injury had forced me to miss most of the 2014 season and I had fallen from second in the world rankings to out of the Top 30. Emotionally, I was very frustrated. It’s very hard to stay patient when you’re out with an injury. One of the things that would take my mind off of tennis for a few hours was watching basketball. (Yes, it’s true, even athletes use sports as an escape from their jobs.) I fell in love with the game of basketball when I came to the U.S. at age 15 and have become a big fan of the Spurs through my friendship with Tony. When I’m overseas, I’ll wake up at ungodly hours to stream playoff games on my computer. Unfortunately, my NBA League Pass subscription is blocked when I’m in Europe or Asia, so I end up having to watch terrible streams from strange websites that I’m sure are giving my laptop a virus. (Come on, NBA. Fix your broadcast rules!)

What’s so interesting to me about basketball is how a team can go to the next level through chemistry and communication. You watch how a team like the Spurs can move the ball around the court with an unspoken understanding, and it’s really beautiful. It’s very different from tennis, where you’re out there all alone. But there is one thing that is so important in both tennis and basketball: You need to be mentally tough in order to stay consistent, because the opponent is always going to go on a run. You’re always going to have a tough stretch in a game or in a season. Discipline is what makes a team like the Spurs so competitive for 15-plus years. And it’s not always easy.

Every time I ask Tony what Gregg Popovich’s secret is, he just smiles and says, “He’s tough.”

Tennis. Basketball. Life. It’s all about mental toughness. Whenever you’re struggling through something in tennis, it can be a lonely experience because there’s no real locker-room environment to fall back on to lift you up. I have been traveling all over the world by myself since I was 10 years old. That “lone wolf” mentality becomes a part of you whether you’re conscious of it or not. I think this issue is especially difficult for female athletes in solo sports like tennis and golf. When you’re a man, you have the freedom to start a family and take your wife and children on the road with you. As a female athlete, you often have to put all that stuff on hold while you’re in your prime.

When you’re on top of your game and everything is going well, it’s easy to ignore this stuff. But when you’re struggling, sometimes you look around at the empty hotel room and you wish that you had the support of a team. That’s why it’s so important to me to have friends like Tony who know what it’s like to go through the long journey back from an injury. Because it’s not just the physical pain of rehab, it’s the mental process of being able to trust your body again. That’s something that I think only other pro athletes can understand.

Tony kept telling me not to take it easy on him at the park. He wanted me to hit it to his backhand (which definitely needs some work) so that he could get better. I kept telling him to bend his knees when he hit the ball, and finally it clicked for him and he really got his entire body into a serve and he legitimately aced me.

He was like, “Did you let me do that? Were you playing for real?”

(I was playing for real, for the record.)

That’s the moment that gives you goosebumps as an athlete, when everything clicks and you do something you thought was impossible. The look on Tony’s face was amazing. He was looking at Boris like, !!!!!!

That little pick-up game was really important for me. I returned from my injury two months later and have slowly made my way back into the WTA Top 30 rankings. Tony and I haven’t had a chance to get back onto the tennis court yet because of our crazy schedules, but I can’t wait.

Just warning you, Tony: I’m tough. Just like Pop.