The Sensex opened 221 points down on Monday as funds and retail investors continued selling on fears of another hike in key interest rates by the RBI to regin in inflation. The 30-share index of the Bombay Stock Exchange that tumbled 868 points in the previous four sessions, slid by another 221 points today to 19,470 level at the openings trade, with all the sectoral indices trading in red. In a similar fashion, the broad-based National Stock Exchange index Nifty fell by 72 points to 5,833 points.