Serena Williams obliterates Karin Knapp to reach Cincinnati Open quarter-finals

Serena Williams has cruised into the quarter-finals of the Cincinnati Open after a devastating 6-0 6-2 thrashing of Karin Knapp.

The world number one demolished her Italian opponent in just 55 minutes, achieving a flawless first set before batting away Knapp's attempts to claw games back in the second set.

Knapp proved less of a challenge than Tsvetana Pironkova, the Bulgarian putting up a fight on Wednesday as the world number one secured a 7-5 6-3 victory.

Williams will take on the winner of Sloane Stephens and Ana Ivanovic.