Serena Williams races into WTA Championship semis in Doha

WORLD number one Serena Williams raced into the semi final of the season ending WTA Championships in Doha, Qatar with a comfortable straight-sets victory over Elena Dementieva.

 HARD HITTING: Serena Williams proves far too strong for Elena Dementieva in Doha

Williams, who returned to the top of the world rankings on Wednesday after Dinara Safina withdrew from the competition, chalked up her third victory in as many matches to top the Maroon Group.

In doing so she also kept sister Venus' slim hopes of qualification alive.

Dementieva got the better of Serena the last time the duo met in Toronto in August, but from the world go, the American was dominant and too powerful for the Russian.

She raced ahead with her booming ground strokes finding their target and took a 6-2 lead.

And while Dementieva rallied in the second set, she came under intense pressure when serving a 4-5 to stay in the match and she found the net on Serena's first break point to hand her opponent victory in one hour and 45 minutes.

"It feels really great, I'm really excited because I never normally do very well at the round-robin format.

"And to win feels good because she has beaten me a couple of times recently and I had felt like I was really close to beating her, but then at the same time really far away.

"I've got a day off tomorrow [Friday] and I'm going to sleep all day because I've been playing every day and I've got doubles to do as well, but I'm really looking forward to it."