The Sensex, which rose to 17,188.55 at opening, fell by 57.60 points to 17,025.09 as stocks of refinery and capital goods segment suffered fresh losses.
The broad-based National Stock Exchange index Nifty fell 14.05 points to 5,118.25, after climbing an intra-day high of 5,160.20.
A firm trend in the Asian region and higher openings in Europe failed to lift the market sentiment.
Brokers said the market took a dip as RIL, which has the heaviest weight on the Sensex, dropped on profit-booking.
Besides, they added, that reports of CLSA - a brokerage and investment group - downgrading RIL to "outperform" from "buy" hit market sentiment.
Moreover, the stock which gained 2.4 per cent on Friday, dropped 3.88 per cent as the market judged RIL's second quarter earnings - announced on Saturday - to be below expectations. IT major Tata Consultancy Services fell 1.30 per cent, ahead of its financial results this evening.
Larsen and Toubro also fell 1.98 per cent.State Bank of India and automakers Tata Motors and Maruti Suzuki bucked the trend and saved the market from a big fall.
The oil and gas sector index suffered the most - down 2.29 per cent to 8,656.95, followed by capital goods (1.37 pc) at 10,891.46. Power index lost 1.18 per cent at 2,142.98 and IT, 0.50 per cent to 5,670.47.
However, auto, consumer durables, banking, realty and FMCG sector indices gained