The Sensex fell by almost 100 points in opening trade today on profit-booking by funds amid a weak trend in the Asian region. The 30-share barometer, which had gained 217 points in the previous session on Thursday, fell by 100 points to 19,765 in the first five minutes of trade. Similarly, the wide-based National Stock Exchange Nifty index also declined by 34 points to 5,914 points.