The Sensex at the Bombay Stock Exchange advanced 187 points, or 1.1 per cent, to 17,027 in opening trade, this morning, on fresh buying by investors, amid rising regional markets. But later, as the regional markets gave up some of their early gains, the Sensex also eased from initial highs, to stand 57 points, or 0.3 percent in positive territory, and slip below the 17,000 level, at 16,897, in afternoon trade, a short while ago.Stock markets in Japan, China, Hong Kong, Singapore and South Korea were trading mixed, today.