Erasing initial gains, the 30-stock index fell for the 5th straight session by losing 211.30 points, or 1.15 per cent to 18,226.48, its lowest level since September 13, 2012.
The gauge rose to 18,565.56 at the outset. In the last four sessions, the Sensex had lost over 603 points.
Similarly, the broad-based NSE Nifty dipped below 5,500 points level by losing 47.85 points, or 0.86 per cent, to close at 5,495.10. The index touched the day's high of 5,603.05 and low of 5,487.00.
They said selling pressure was strong despite firming global trend.
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"Widespread selling, led by IT and oil and gas sector stocks, dragged down the Sensex to over seven-month low," said Deepak Pahwa, a Delhi-based stock broker.
Shares of Wipro slumped 12.19 per cent to Rs 393.80 on the first day of trade as a standalone IT stock after the company hived-off its three non-IT business divisions into a privately-held company.
Bucking the trend, stocks of TCS ended 1.10 per cent higher at Rs 1,497 after company said it will acquire France-based enterprise solutions provider Alti Sa.
ICICI Bank, Jindal Steel, NTPC, Sun Pharma and Tata Motors found some support and managed close in positive zone.
The IT sector suffered the most by losing 2.10 per cent to 6,524.71 after Infosys tumbled by 2.36 per cent to Rs 2,766.35, followed by PSU sector index by 1.57 per cent to 6,399.72. Oil and gas index lost 1.65 per cent to 8,323.28, Banking index by 0.82 per cent to 12,538.86 and Consumer Durables index by 1.20 per cent to 6,937.58.