(Adds background) By Martyn Herman RIO DE JANEIRO, Aug 16 (Reuters) - Elia Viviani's Olympic gold medal hopes seemed to have vanished in a tangle of legs and carbon fibre after a crash during the finale of the men's omnium but the Italian recovered to claim an emotional victory on Monday. Clambering back to his feet after the mid-race mayhem that left South Korea's Park Sanghoon in hospital, Viviani kept his wits about him during the rest of the 160-lap points race -- the sixth and final element of the two-day event. Britain's Mark Cavendish, culpable for the crash, chipped away at Viviani's lead in the standings, as did charging 2012 champion Lasse Norman Hansen of Denmark, but Viviani showed admirable composure in the heat of an attritional battle. More...