Stock market benchmark indices Sensex and Nifty tumbled in early trade on Friday after a five-day rally, dragged by heavy selling in IT firms following revenue growth guidance cut by Accenture.The 30-share BSE Sensex tanked 786.58 points to 76,624.90 in early trade. The 50-share NSE Nifty declined 210.95 points to 23,959.80.From the 30-Sensex firms, Infosys dived over 8 per cent, Tata Consultancy Services tumbled 6 per cent, Tech Mahindra traded 5 per cent lower and HCL Tech declined 4.9 per cent. HDFC Bank and Tata Steel were also among the laggards.NTPC, Bharti Airtel, Trent and Power Grid were among the winners.The BSE IT index dropped 5.38 per cent.Brent crude, the global oil benchmark, traded 0.93 per cent lower at USD 79.11 per barrel.In Asian markets, South Korea’s Kospi and Japan’s Nikkei 225 index quoted marginally higher.US markets ended higher on Thursday.