By Steve Gorten

KEY BISCAYNE – Andrea Petkovic is admittedly very uptight when it comes to her job as a professional tennis player.

“I’m just very stiff German,” she said with a smile Tuesday after becoming the first to advance to the women’s semifinals of the 2015 Miami Open.

Translation: Petkovic is a perfectionist.

But in her personal life, the 27-year-old German, ranked No. 10 in the world, is the “total opposite.” She’s a novice art collector who enjoys going to museums, joking around, reading, writing, and dancing.

She also loves going to basketball games as much as the rapper, Drake, whose song, “Truffle Butter,” happens to be her current favorite.

It’s always been a struggle for her to find the right balance between her two sides, she said, and she expects it to be that way all her life. But Petkovic has managed to find “a golden line” as she has aged, and Miami seems to mesh her personalities with ease.

It’s why she enjoys playing at the Miami Open so much, and continues to have success here. Tuesday, the ninth-seeded Petkovic beat 14th-seeded Karolina Pliskova of the Czech Republic 6-4, 6-2 in 75 minutes, to move on to the semifinals for the second time.

She has yet to lose a set in four matches here this year, beating Christina McHale, Kristina Mladenovic, and the world’s ninth-ranked player, Ekaterina Makarova, prior to Tuesday.

Petkovic also reached the semifinals at Crandon Park Tennis Center in 2011, when she lost to Maria Sharapova in three sets. She has reached the round of 32 in two of her three other appearances at this tournament.

“In my job, I’m just very straightforward and disciplined. With the discipline comes a lot of tightness as well,” Petkovic said. “Miami definitely relaxes me. I don’t know, maybe because it’s kind of crazy and chaotic. Those two opposites, they sort of mesh into a balance that’s good for me, I guess. It’s the same in Paris where I also feel very comfortable. The city relaxes me. That’s very important for me.”

Added Petkovic, who lost her opening match at Indian Wells earlier this month: “For example, I’ve never played well in Indian Wells maybe because everything is so…”

Pristine?

“Yeah. And very clean,” she said. “Then I get into my complete German mode, and that’s not good for me, actually.”

Petkovic smiled again. She said she’s “definitely a total stereotype of a German,” and proud of it. Her passion for perfection on the court has helped her become one of the world’s top tennis players. But Petkovic, whose parents are from Serbia, also has “this fiery side of me” that’s fun-natured.

“My two idols that I grew up with were Steffi Graf, who is the stereotypical German, and Serena Williams, who is probably the opposite…who is just that rebellious, rock ‘n roll type of tennis player that brought new energy, something new to tennis and to the WTA,” Petkovic said. “Steffi Graf was so disciplined and so controlled emotionally. I just admire them. I wish I could have five percent of either one. I would be a very happy girl.”

Finding the right mix of concentration and relaxation is one of the tougher challenges for a pro athlete, Petkovic added.

“Especially for tennis players, because it’s so much mentally,” Petkovic noted. “And there are players, when you see them hitting the ball, you wonder why they are not in the top 10, and you cannot even find them in the top 100. It’s because it’s such a difference between practice and matches and being able to find the right balance for yourself.”

“Everybody is so different, and there is not a golden formula that you can give a tennis player and say, ‘OK, these are the right things to do.’ Everybody has to find it for themselves.”

Petkovic lost the opening match of her first three tournaments this year, and had dropped three of her past five matches coming into the Miami Open. She was so stressed on the court, she said, it felt like she was “in a full-body cramp.”

“I have my tricks now to get out of it,” she noted, “but I cannot share them with you. …It’s not child-friendly.”

Against Pliskova on Tuesday, Petkovic led 4-1 to start the match. Then she lost three consecutive games and faced double-break point serving at 4-4. The sun was affecting her ability to see the ball on her toss, and she had lost her rhythm serving.

But Petkovic managed to pull through, winning five consecutive games from that point to seize control of the match.

“I just sort of shoved it aside and I thought, ‘Andrea, you can’t think about your serve too much. Just throw the ball up and hit it, and if it goes in, good for you,’” Petkovic recalled. “That’s what I did, and I regained a little confidence in my serve. I served tremendously in the second set then.”

Recently, Petkovic bought her first piece of fine art – something from Swedish artist Jacob Fellander. Now, she’s interested in buying something from a French impressionist, she said. Her winnings in Miami this year should help cover the cost.

“I didn’t know if I should do that before,” she said. “But now that I play in the semifinals, I think I want to buy it. I just hope it’s still available.”