Williams wins Cincinnati Masters

Serena Williams has tuned up for the US Women's Open in perfect fashion with victory over Simona Halep in the Cincinnati Masters.

Serena Williams has won the Cincinnati Masters, beating Romania's Simona Halep in straight sets. (AAP)

Serena Williams has won the Cincinnati Masters, beating Romania's Simona Halep in straight sets in the final.

The world No.1 beat the No.3 seed 6-3 7-6 (7-5), enjoying a perfect build-up to the US Open.

Williams is bidding for history at the US Open as she attempts to complete a rare calendar-year Grand Slam singles sweep.