At the pre-opening bell on Thursday, the frontline index S&P BSE Sensex opened in red with a loss of 265.68 points or 0.35%. Sector-wise, in the pre-opening session, metals dropped by 0.18%, power plunged by 0.15%, and auto slipped by 0.27%. Meanwhile, KSB Ltd, Supreme Petrochem Ltd and Avantel Ltd emerged as the top gainers of BSE in the pre-opening session.