The Sensex opened 140 points down on continued selling by foreign funds and retail investors amid weak trend in Asian bourses. The 30-share barometer, which has lost 250 points in the previous four sessions, moved further down by 140 points to 19,311 level, led by the fall in auto, realty, metals, IT and banking stocks. Similarly, the wide-based National Stock Exchange index Nifty slid 37 points, down to 5,805 points.