Serena Williams: Sharapova on her toughest opponent

Terming Serena Williams as toughest competitor she's ever faced, ex-world number one Maria Sharapova said the 23-time Grand Slam champion was the most challenging and consistent in her level. Serena has a 20-2 career record over Sharapova. She won the last 19 meetings in a row. Notably, it's the longest active winning streak over a single player on WTA Tour.