Venus Williams made certain of reaching the last four of the WTA Championships with a landslide 5-7, 6-1, 6-0 victory over sister Serena Williams here on Thursday. The result brought the first love set between them in any of their 18 WTA Tour matches and twice reduced the younger sibling to tears. The Wimbledon champion's win over the US Open champion was her third in three days, enabling her to finish her top of her round robin group, and ensuring that she joined Jelena Jankovic and Vera Zvonareva in the knock-out semi-finals of the women's season-ending event. But Serena, who has only one win, will need to beat Olympic champion Elena Dementieva on Friday if she is to be sure of keeping alive the chances of an all-Williams final.