The market sentiment was affected adversely by data showing that foreign portfolio investors (FPIs) were net sellers of Indian stocks on last Friday.
They sold shares worth a net Rs 723.48 crore, says provisional data from the stock exchanges.
The Sensex opened slightly higher at 25,093.16 and moved up further to 25,095.76.
However, it declined immediately to 24,915.93 before quoting at 24,991.69 at 1000 hours, showing a loss of 32.66 points, or 0.13 per cent, from its last weekend's level.
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Other losers were Coal India (1.99 per cent), SSLT (1.70 per cent), Bharti Airtel (1.51 per cent) and Sun Pharma (1.15 per cent).
However, Asian markets edged higher in their early trade as euro zone banking jitters faded.
Key benchmark indices in South Korea, China, Taiwan, Hong Kong and Japan rose by 0.26-0.38 per cent while Singapore market fell by 0.29 per cent.