Serena Williams makes light work of Mona Barthel

Serena Williams has breezed into the quarter-finals of the Cincinnati Open with a 6-4 6-1 victory over Mona Barthel.

The world number one never looked in trouble on Centre Court, although the German did manage to get a break of serve in the first set.

It was not enough to stop Williams taking it 6-4 and then wrapping up the second 6-1 without giving the 23-year-old a sniff at break point.

The American will face Simona Halep for a place in the semi-finals.