Two things you can count on

Caroline Wozniacki will get at least one walkover or retirement during a tournament.

Victoria Azarenka will wind up lying on the court, limping off of it, or both.

In today's BNP Paribas Open quarterfinal, we got it all. Top seed Wozniacki played her friend Azarenka, and after only three games, Azarenka sustained a left hip flexor strain, and--after being advised by her coach--retired from the match.

Azarenka has struggled repeatedly with hip and thigh injuries. She went through a famous food poisoning (still wrongly labeled "heat illness" by the press) incident, and an even more famous incident in which she passed out on the court after getting a concussion before the match. As for Wozniacki, she is so often the recipient of retirements and walkovers, I've come to expect one every tournament.

In the last of the quarterfinal matches, Maria Sharapova and Peng Shuai went three sets, and Sharapova prevailed, 6-2, 5-7, 6-3. And though it still sounds odd to say it, Sharapova is seeded 16th.