LONDON, Dec 17 (Reuters) - The poster child of China"s property crisis China Evergrande Group (3333.HK) was officially declared in default by credit rating agency S&P Global on Friday after the sprawling firm missed a bond payment earlier this month. "We assess that China Evergrande Group and its offshore financing arm Tianji Holding Ltd. have failed to make coupon payments for their outstanding U.S.-dollar senior notes," S&P said in a statement. S&P added that Evergrande had asked for the ratings to be withdrawn following the downgrades to "selective default" a term ratings firms use to describe a missed payment on a bond, but not necessarily all its bonds. "Evergrande, Tianji, or the trustee have made no announcement or any confirmation with us on the status of the coupon payments," S&P said.