The Sensex rose for the third straight day in the last trading session of the year. It advanced by another 120 points to reach 20,509 on sustained buying. Brokers said, the Sensex ended the year by becoming the best performer in the Asian region during 2010. The National Stock Exchange index Nifty rose by 32.65 to 6,134.50, after touching the day’s high of 6,147.70 as stocks in realty, banking and auto segments gained on strong buying.