Serena powers into Miami semi-finals, Murray advances

MIAMI, March 29 (Reuters) Serena Williams stayed on course for a fourth Sony Ericsson Open title with a ruthless 6-1 6-4 win over Czech Nicole Vaidisova in the quarter-finals.

On the men's side, Briton Andy Murray reached the semi-finals when his opponent Andy Roddick was forced to retire with a hamstring injury trailing 5-3 in the first set.

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

Playing her first tournament since lifting her eighth Grand Slam title at the Australian Open, Williams has grown in 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 yesterday.

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.

Murray, the 12th seed, was leading 4-3 when American Roddick called for a medical timeout to receive treatment in the locker-room.

The third seed returned to the court but was immediately broken and the 2004 champion walked to the net to shake hands and informed the umpire he could not continue.

''I don't know what it is, I'm going to get an MRI, I think the medical term is, the bottom of my ass hurts,'' Roddick said.

''He hit a volley behind me and I lunged at it and hurt something.

''It's disappointing but right now I just want to focus on getting better.'' The 19-year-old Murray moved into the semi-finals for the second successive Masters Series event having reached the last four at Indian Wells.

''I guess anybody would rather get off the court quicker than longer but I'd rather it was under normal circumstances,'' said Murray. ''I'm definitely going to have enough time off to be 100 percent fit going into the match.

''I've lost my last two Masters semi-finals and I'd like to get to my first final.'' REUTERS AD BST0735