Serena Williams marches on in Cincinnati

World number one Serena Williams has swept aside Tsvetana Pironkova in straight sets to maintain her pursuit of a second successive Cincinnati Open title.

The reigning champion secured a 7-5 6-3 victory in 90 minutes to advance into the third round, where she will meet Karin Knapp.

Nothing could separate both players in a cagey first set that saw the duo hold their respective serve en route to being deadlocked at five games apiece.

However, the American won on her serve, before breaking Pironkova - ranked 43rd in the world - to edge out her Bulgarian counterpart in the opening set.

The second set looked poised to follow a similar pattern, with neither player managing a break of serve for seven games, but Williams pulled one out in the eighth to earn the daylight needed for victory.