Investors also focussed on oil prices and the West Asian crisis and reacted to the September quarterly earnings of heavyweights such as Idea Cellular, L&T and Coal India.
The 30-share index resumed positive before slipping to 33,176.67, down 137.89 points, or 0.41 per cent, at 1122 hours.
The broader NSE Nifty traded lower by 55 points, or 0.53 per cent, at 10,266.75.
Major losers were L&T, Coal India and Cipla, sliding up to 2.95 per cent.
Overseas, Asian markets saw a mixed trend. US stocks closed mostly lower last Friday as they snapped multi-week winning streak while some of the largest technology stocks pulled back.
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