Barthel broke twice to give her the opportunity at 4 - 3 to get back on serve .
Williams capitalised on the German also having trouble with the sun to break back then served out from the Yarra River end to clinch the first set in 42 minutes .
Barthel broke twice to give her the opportunity at 4 - 3 to get back on serve but Williams capitalised on the German also having trouble with the sun to break back then served out from the Yarra River end to clinch the first set in 42 minutes .