British rider Tom Pidcock staged an extraordinary comeback from a puncture to win his second straight mountain biking Olympic gold Monday, holding off French home favourite Victor Koretzky in a thrilling sprint finish. Pidcock celebrates his 25th birthday on Tuesday but the tyre mishap threatened to spoil the party, dropping him down from first to ninth place, 40 seconds off the pace. But he picked his way through the field after a ponderous tyre change to bring himself back into contention just behind Koretzky, who was being roared on by a partisan home crowd. Overhauling Koretzky with metres to spare in a helter-skelter dash for the line, Pidcock could scarcely believe what he had done.