A weak rupee and tepid global cues ahead of US GDP growth data and European Central Bank's rate decision, also affected the domestic market sentiment.
Shares of Realty, Consumer Durable, Banking, Power, PSU, Capital Goods and Auto fell while IT and metal rose.
The Sensex opened higher and moved up to a day's high of 21,142.85 on initial buying on the back of capital inflows.
The S&P, which affirmed the rating on India at 'BBB-/A-3' and retained negative outlook, triggered a wave of selling in the last 2 hours as investors were spooked by downgrade fears.
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"Markets showed signs of panic selling in the afternoon. While the rating agency affirmed the current rating, it warned of a likely downgrade in 2014 if the new government fails to reverse India's low growth," said Milan Bavishi, Head Research, Inventure Growth and Securities.
The Sensex has now lost over 417 points in the past three days in stark contrast to the jubiliant mood after the index closed at all-time high of 21,239.36.On Sunday.
Similarly, NSE index Nifty fell by 27.90 points to end at 6,187.25. Also, SX40 index of MCX-SX fell by 23.07 points.
Among the 30 Sensex constituents, 17 stocks fell led by RIL, SBI, ICICI Bank, BHEL, Bharti Airtel and Tata Motors.
The rupee also fell to the lowest level in 5 weeks by plummeting to 62.73 per dollar and was last trading at 62.5.
In Asia, barring Taiwan, which moved up marginally, other indices of China, Hong kong, Singapore, Japan and South Korea declined. European stock markets also moved lower.