Serena Williams steamrolled Samantha Stosur 6-1 6-1 on Saturday to reach the final of the WTA tour’s green clay Charleston tournament.

Williams needed just 59 minutes to subdue the second-seeded Australian, who beat the American in the US Open final last September but has lost to her twice in the past fortnight.

Williams, seeded fifth, improved to 6-3 overall against Stosur, including a straight-sets victory in Miami 11 days ago in which Williams fired 20 aces.

Williams had a relatively sedate seven aces on Saturday, but she saved both break points she faced and broke Stosur five times as the Australian failed in a bid to become just the eighth player to beat both Williams sisters in the same tournament.

Stosur defeated Venus Williams in the quarter-finals to spoil the chance of an all-Williams semi.

Serena Williams awaits the winner of the second semi-final between ninth-seeded Czech Lucie Safarova and 14th-seeded Polona Hercog of Slovenia.

Hercog, who surprised third-seeded Marion Bartoli in the third round, advanced Friday with a victory over 2006 Charleston champ Nadia Petrova.

The victory over Bartoli, ranked seventh in the world, was world No.38 Hercog’s first career victory over a top-10 opponent.

The 21-year-old owns one career WTA title, but is in the semi-finals of one of the WTA’s premier level events for the first time.