Friendly rivalry revived

Andrea Petkovic celebrates her win over Danka Kovinic in the quarterfinals Friday April 11, 2105 at the Family Circle Cup on Daniel Island. Grace Beahm/Staff

Andrea Petkovic and Angelique Kerber first played against each other when they were just kids, on the junior tennis circuit in their homeland of Germany.

“I used to lose to her all the time,” Petkovic said of her countrywoman. “I lost to her I think 25 times. I couldn’t even win a game.”

The 27-year-old Germans — known as “fräuleinwunder” at home — are on more equal footing these days. Petkovic, the third seed and defending champion, will meet No. 5 seed Kerber in the Family Circle Cup semifinals Saturday after hard-fought victories Friday.

Petkovic, ranked No. 11, lost a first set for the second time this week and rallied for a 2-6, 6-3, 6-1 win over qualifier Danka Kovinic. Kerber, ranked No. 16, was down 1-5 in the first set before staging her own comeback for a 7-6 (4) , 7-6 (3) win over No. 13 Irina-Camelia Begu.

Earlier Friday, No. 7 seed Madison Keys overwhelmed fellow American Lauren Davis, 6-2, 6-2, to earn her first Family Circle Cup semifinal in three visits to Daniel Island. She will face qualifier Lucie Hradecka, who is ranked No. 110 and scored a 6-2, 6-4 upset of No. 14 Sara Errani in Friday’s quarterfinals.

Kerber and Petkovic will meet for the 10th time; Kerber leads the head-to-head series 6-3 over her friend, but Petkovic has won the last three.

“Angie is one of the few people to whom I would entrust absolutely any secret,” Petkovic has said. For her part, Kerber credits Petkovic with pulling her out of a funk a few years ago, helping her to the semifinals of the U.S. Open in 2011.

“Without Andrea, I wouldn’t be where I am today,” Kerber said during Fed Cup play last year. “She pulled me from a deep hole I had climbed into.”

Now, Kerber must beat her friend in order to win her fourth WTA singles title; Petkovic seeks her seventh. They haven’t played a tour match since 2011.

“You need to try to put the emotion outside,” said Kerber. “But I think we know each other so well that it doesn’t matter what happens on court. Tomorrow we will still be friends. One of us will win, and we will try to give our best and the better will win tomorrow. Let’s see.”

Petkovic was at less than her best against Kovinic, slamming her racket to the green clay after losing the first set. Her mother immediately left the box; Mom did not approve.

“I definitely know why she left the box,” an abashed Petkovic said. “And that’s OK. Sometimes, it does help me when I get really angry. It’s better than getting disappointed and feeling sorry for yourself.”

At the start of the second set, Kovinic — a 20-year-old from Montenegro ranked No. 121 — made some unforced errors that helped Petkovic get back into the match.

“She gave me a few presents, and then I found my rhythm,” she said. “I sort of snapped my teeth into the game again.”

The 29-year-old Hradecka has been snapping her teeth into healthier food to boost her career. She’s a seasoned veteran who has won more $3.4 million in her career, and she’s dangerous on clay. More than half of her 75 career main-draw wins have come on clay, and she’s reached six WTA finals in her career, four of them on clay.

Saturday’s semifinal against Keys will be Hradecka’s seventh match in eight days, as the Czech had to qualify for the Family Circle Cup. But a new diet might give her an energy boost against the 20-year-old Keys. Hradecka avoids gluten, dairy and eggs. It must help; she’s 22-7 in singles this year.

“In the beginning, it was tough to choose food, because egg and milk you have everywhere,” she said. “But I’m used to it, and it looks like it works, so I’m fine with this.”