By Clare Jim and Anshuman Daga and Kane Wu Reuters (Adds investor quote in paragraph 19 and details of SEC chair comment in paragraph 33) HONG KONG/NEW YORK, Sept 21 (Reuters) – Persistent default fears eclipsed efforts by China Evergrande Group's chairman to lift confidence in the embattled firm on Tuesday, as Beijing showed no signs it would intervene to stem any domino effects across the global economy. Analysts played down the threat of Evergrande's troubles becoming the country's "Lehman moment," though concerns about the spillover risks of a messy collapse of what was once China's top-selling property developer have…