DOHA: Serena Williams won her second career WTA Championship title on Sunday with a commanding 6-2, 7-6 (7/4) victory over sister Venus, a triumph which earned her a $1.55 million. It was Serena's second season-ending trophy to add to her 2001 success and made 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 No 1 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 win was Serena's 13th victory in 23 meetings with her sister, a family rivalry stretching back to 1998. 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, treated several times during her gruelling 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.