The BSE benchmark Sensex fell by over 81.43 points in the opening trade today on emergence of profit-booking at higher levels amid weakening Asian trend. The 30-share index, which had lost 109.62 points in the previous session, fell by 81.43 points, or 0.43 per cent, to 18,600.88 in first five minutes of trading.Similarly, the wide-based National Stock Exchange Nifty Index shed 26.20 points, or 0.46 per cent, to 5,758.05.