Serena Williams secured the season-ending World No. 1 ranking yesterday. Today, she stormed past Elena Dementieva, 6-2, 6-4, to seal a semifinal spot in the season-ending Sony Ericsson Championships in Doha along and earn an added bonus in the process — a day to sleep in.

"It feels good to be through because I've never really done well in this round-robin format," said Williams. "Tomorrow I'm going to sleep all day because I've played every day so far here and I'm really tired."

It was the third consecutive win for Williams, who fought off a match point to subdue sister Venus, 5-7, 6-4, 7-6(4) on Wednesday. Williams, who saved set points to top reigning Roland Garros champion Svetlana Kuznetsova in Tuesday's opening day of play, finishes round-robin play with a 3-0 record in the Maroon Group. Caroline Wozniacki, who survived cramps and Vera Zvonareva to raise her round-robin record to 2-0, has qualified for the semifinals from the White Group leaving two spots open in the final four.

Williams cruised through the opening set, breaking in the sixth and eight games and firing a forehand winner crosscourt to collect the first set.

The 11-time Grand Slam champion broke for a 2-0 second-set lead, but Dementieva, who had rallied past Venus in her first match, immediately broke back in the third game with an inside-out forehand winner.

Dementieva's serve deserted her as she served to extend the second set. The Russian, who overcome 15 double faults against Venus, dumped her 10th double fault to hand Serena triple match point. Williams could not convert the first two but ended the match when Dementieva's forehand stuck in the net.

Williams won the 2001 season-ending Championships when Lindsay Davenport conceded a walkover in the final. She lost to Kim Clijsters in the 2002 final and to Maria Sharapova in the 2004 final.

Asked her reaction to Andre Agassi's admission that he used crystal meth in his new book, Williams took the time to plug her own memoir.

"I don't even know what crystal meth is so, you know, that's what my reaction to it is. I haven't read anything about Andre Agassi's book," Williams said. "All I know is that I have a book coming out."