PARIS (AP) -- Andrea Petkovic had plenty to be philosophical about when she considered retiring from tennis after a succession of injuries saw her drop out of the top 10 and plummet to 143rd.
Fast forward 18 months, the 26-year-old German is into a Grand Slam quarterfinal again after beating unseeded Kiki Bertens 1-6, 6-2, 7-5 at the French Open on Monday.
It's her first quarterfinal at a major since she reached the last eight at the U.S. Open in 2011. Petkovic also reached the quarters at the Australian Open and French Open that year, achieving a career-high ranking of No. 9.
Then it all started to go wrong. Injuries to her back, ankle and knee took their toll, and by the end of 2012 she was ranked 143rd and missed five of the eight Grand Slams in 2012 and 2013.
With her career turning into a nightmare, she started looking elsewhere.
''I asked for some internships at newspapers,'' said Petkovic, seeded 28th at Roland Garros. ''I was also writing for kind of a big newspaper in Germany for a while, and I asked a few politicians that I know if I could do an internship with them.''
Although her career is back on track, she has taken classes in political science, philosophy and literature. So she knows what to do when she's in a philosophical mood: pick up a book.
Petkovic considers Johann Wolfgang von Goethe ''our greatest genius with words'' and admires the works of Friedrich Nietzsche.
''Philosophy-wise, Nietzsche is the one that impressed me most. I don't necessarily agree with everything he says and it's very dark and sad, but he was a good writer,'' she said. ''I actually really liked the existentialists in French. I read a lot of (Jean-Paul) Sartre and (Albert) Camus.''
Although she loves learning, Petkovic has ruled out a future career in teaching.
''I would love to be able to do that, but I have no patience whatsoever,'' she said.
Petkovic had plenty of time to think in the early days of her career when she would travel on her own and stay in cheap places.
''That was a good lesson of life being in all these little villages,'' she said. ''It made me tougher.''
One memory stands out.
''Once, when I played in England, the hotels were so expensive and I had just finished school. I stayed at a hostel and next to me were 25 boys celebrating something,'' she said. ''They kept singing English songs for the whole night. And I had to play next day at 10 in the morning. ... Well, I lost.''