The American 16-time Grand Slam winner will now play Czech Republic third seed Klara Zakopalova who had little trouble eliminating Dutch hope Richel Hogenkamp 6-2, 6-3.

Williams broke her opponent's serve three times in each set and was never in trouble on her way into the final four.

Williams leads Zakopalova in their head-to-head, 3-1, but while the American won their first two meetings handily during the 2003 season, they went 1-1 in their last two meetings during the 2009 clay court season, Zakopalova winning in the first round of Marbella and Williams winning in the first round of the French Open.

The second semi-final will pit home favourite Johanna Larsson against Italian Flavia Pennetta after both players won their quarter-final matches in straight sets.

The 24-year-old Larsson, who is looking for her first WTA singles' title, dropped just three games on the way to a 6-1, 6-2 thrashing of Frenchwoman Mathilde Johansson.

Pennetta who reached the fourth round at Wimbledon, and had a career high world ranking of 10 in 2009, also made short work of her French opponent with a 6-1, 6-3 victory over veteran Virginie Razzano.

The 31-year-old from Brindisi won the doubles titles in Sweden along with Gisela Dulko in 2009 and 2010 as she chases her first single's title at Bastad and 10th WTA victory.

Pennetta and Dulko also teamed up to win the Australian Open doubles' crown in 2011. (AFP)