Azarenka is serving bad.
She had been broken 19 times since the beginning of the US open.
OK, WTA players get broken more than men, but still 19 times for a top 5 player, that's bad, Serena will destroy her.
"Federer is great on clay, Nadal isn't good on hard court." TMF, december 2014. (Federer 1 slam on clay, Nadal 3 on hardcourt)