DOHA (AFP) Serena Williams won her second career WTA Championships title on Sunday with a commanding 6-2, 7-6 (7/4) victory over sister Venus, a triumph which earned her a cool 1.55 million dollars. Serena, who will finish the season as world number one, also won the trophy in 2001, making her just the second player after Justine Henin in 2007 to win two Grand Slam titles as well as the WTA Championship in the same year. World number one Serena won all five matches at this event, including a group stage win over Venus, and such was her dominance in the final that she gave up just seven points on serve. The 85-minute romp was Serenas 13th victory in 23 meetings with her sister, a family rivalry stretching back to 1998. It feels fantastic. I definitely wasnt expecting to win when I came here because I hadnt been practicing very well, said Serena. I kept fighting against a really tough player but Venus kept hitting the ball back. Thats never easy and its really frustrating. In a symbol of this injury-hit, desert money-spinner, which had seen four players end their campaigns prematurely through various aches and pains, both sisters arrived on court nursing knocks. Serena had her left thigh heavily-strapped while Venus had protection on her left knee which was treated several times during her semi-final win over Jelena Jankovic. But Serena, with four wins from four matches here, was the fresher of the two in the first set, a legacy of having spent three and a half hours less than her sister in reaching this stage. Breaks in the third and seventh games gave the new world number one the opening set. Serve dominated the second set before Serena stretched to a 5-2 lead in the tie-breaker. An ace set up match point and the title was secured with a crunching forehand winner. Victory added to Serenas capture of the Australian Open and Wimbledon titles in 2009. The WTA Championships, being held here for the second of three years before they switch to Istanbul in 2011, were hit by a series of worrying injuries, all coming at the end of another gruelling year. Dinara Safina saw her world number one spot swept away by the flood of tears which accompanied her withdrawal because of a back injury after just two games and 12 minutes on court against Jankovic. Caroline Wozniacki, who overcame crippling cramps to beat Vera Zvonareva, was forced to quit her semi-final against Serena to avoid further damage to her thigh and side. The Danish teenager played 90 matches in 2009. Victoria Azarenka was also unable to complete a match, handing victory to Agniezska Radwanska, who had herself started the week as the second alternate but replaced Zvonareva who had moved into the draw instead of Safina.