Mats Wilander looks at how Serena Williams's serve and comes to the conclusion that she is virtually unbeatable.
Serena breezed past Sorana Cirstea 6-0 6-2, extending her winning streak to 27 matches and laying down a marker of her title potential.
The American has dropped a mere six games, and Wilander believes that her power and repertoire of different serves makes her a truly formidable opponent.
"Can she be beaten? Her serves make sure that she is always on the front foot and attacking, which makes life pretty impossible for her opponents," he said.
"There is no doubt that her serve is way above the others on the WTA Tour and she is pretty unbeatable right now, even on clay."