The Sensex at the Bombay Stock Exchange fell 66 points, or 0.4 per cent, to 18,161 in opening trade today. Remaining subdued, the Sensex stood 68 points, or 0.4 per cent in the red, at 18,159, a short while ago.Key stock indices in Japan, China, Hong Kong, Singapore and South Korea were trading mixed today. The US Dow Jones Industrial Average had ended 0.7 per cent overnight.