DOHA, Qatar (AP):

Serena Williams became the first player to clinch a spot in the semi-finals of the Sony Ericsson Championships after beating Elena Dementieva 6-2, 6-4 yesterday for her third straight win in the group phase of the tournament.

Williams was broken to trail 1-2 in the first set but then won seven straight games to take control of the match, moving the Russian around the court with her powerful ground strokes.

'Finally!'

She converted her third match point when Dementieva sent the ball into the net, then pumped her fist and yelled "Finally!"

Williams, who secured the year-end No. 1 ranking after Dinara Safina pulled out with a back injury, has failed to get out of the round-robin phase of the season-ending tournament the last two years.

"I'm happy to finally do well," she said.

Earlier, Caroline Wozniacki overcame severe leg cramps and a tenacious Vera Zvonareva to win 6-0, 6-7 (3), 6-4.

Medical time-outs

Wozniacki needed two medical time-outs to treat her cramping left thigh in the third set and collapsed to the court sobbing and clutching both legs after netting a forehand at 30-15 in the last game. But she got back up and clinched the win when Zvonareva, who had saved two match points in the second set, netted a forehand on the third.

"I have absolutely no idea how I pulled it through, but I'm very happy about it," Wozniacki said.

It was the US Open finalist's second win in the tournament, putting her on the verge of the semi-finals.

Wozniacki said her leg started cramping at 3-1 in the third set.

"From there, it just got worse and worse," she said. "I'm feeling better now. I got to cool down, getting some massage. ... I'm going to do everything tonight to recover to be ready for tomorrow."

The lucrative Doha tournament is the last WTA Tour event of the season for the eight top-ranked women, with the top two players from each group advancing to the semi-finals. The winner pockets up to US$1.55 million depending on her results in the group phase, where each win is worth US$100,000.