Sensex opened lower by 121 points on Wednesday as investors sold stocks amid a weakening global trend. The 30-share index, which lost 126.86 points in the previous session, fell further to 17,629 points in the first five minutes of trading. Similarly, the wide-based National Stock Exchange index Nifty declined by 11.65 points, to 5,304.90 points at the same time. Marketmen said investors and foreign funds were squaring up their pending positions ahead of settlement in derivatives segment on Tuesday. They said weak trend in overseas markets further fuelled the downtrend. Japan's Nikkei traded lower by 1.43 per cent while Hong Kong's Hang Seng index by 0.42 per cent in early trade.