The key benchmark indices opened weak extending yesterday's sharp losses following a setback in global equities on renewed worries over a prolonged global economic recession. Sebi's decision to tighten margins in derivatives segment also weighed on the market. Banking stocks fell despite Reserve Bank of India's latest effort to infuse liquidity in the banking system by cutting cash reserve ratio for the third time in last 10 days. Realty stocks were hit hard. The market breadth was weak as selling was witnessed across the board.