Andy Murray defeated seventh seed Marin Cilic 6-3, 6-2 in their Group clash for his first victory after climbing to the top of the world rankings at the ATP World Tour Finals in London's O2 Arena."A big thank you for all of the support, it was an incredible atmosphere today," Murray said after the match on Monday, Xinhua news agency reported. "I really appreciate it," he added.Murray added 200 points with his 12th win over Cilic and now has 11,110 points in the world rankings as he battles Novak Djokovic (10,980) for year-end No. 1.Enjoying a career-best year, Murray is now 73-9 with eight titles overall and has extended his winning streak to 20 matches since Sept. 20. He will next play Nishikori on Wednesday.Murray broke twice to take a 3-1 lead while Cilic, who committed 17 unforced errors, looked for a second break, but Murray was able to clinch the 46-minute opener.In the second set, Murray broke twice in a run of five straight games to wrap up victory in 90 minutes.