COMMENT | Tennis star Ana Ivanovic has played on all surfaces, including clay, grass, and hard courts. She has even played in an empty swimming pool.

Growing up in war-torn Serbia, Ivanovic would hone her game in the winter at a club with an Olympic pool.

“There were tough times, especially in 1999, during the bombings,” she said. “I thought it would be impossible to continue (playing tennis) because we didn't know how long it would last...