Williams on course

After disposing of top seed Maria Sharapova in the fourth round, Williams made quick work of Vaidisova, overwhelming the 17-year-old in just 67 minutes to advance to the last four.

Playing her first tournament since lifting her eighth Grand Slam title at the Australian Open, Williams has gained form and confidence with every match, underlining her determination to return to the top of the world rankings.

Williams raced through the opening set but met resistance in the second when the eighth-seeded Vaidisova threatened to seize control, securing triple break point at 4-4.

But the young Czech failed to capitalise and Williams immediately made her pay, recording the decisive break to go up 5-4 and winning 13 of the final 14 points to close out the match.

"I play tough when I'm down, I can always count on my serve," Williams told reporters.

Williams will next meet 14th seed Shahar Peer of Israel who booked her place in the final four with a 6-0 6-3 rout of Italy's Tathiana Garbin.

World number one Justine Henin of Belgium will take on Russian ninth seed Anna Chakvetadze in the other semi-final.