The Bombay Stock Exchange benchmark Sensex rose by nearly 173 points in the opening trade on Monday on the back of buying by funds and retail investors amid a firming trend on other Asian bourses.The 30-share barometer, which lost 83 points in the previous session, recovered sharply by nearly 173 points, or 0.92 per cent, to 18,936 as investors accumulated oil and gas, banking, auto and metal sector stocks.Similarly, the broad-based National Stock Exchange index Nifty moved up by 49 points, or 0.86 per cent, to 5,676.