Sensex closed at 80,787.30, up 76.54 points or 0.09 per cent. The 30-share index opened the session with a decent gap-up at 80,904.40 against the last session's closing of 80,710.76, buoyed by GST rationalisation and bullish momentum in auto and metal stocks. The index jumped around 400 points to hit an intraday high at 81,171.38.