Primoz Roglic was poised to win his first Giro d'Italia title after snatching the overall lead from Geraint Thomas with victory in the 18.6-kilometre individual time trial from Tarvisio to Monte Lussari on Saturday.
Jumbo-Visma rider Roglic overcame a mechanical issue to clock the best time of 44 minutes and 23 seconds in the penultimate 20th stage as Thomas (Ineos Grenadiers) faded in the final metres, crossing the line 40 seconds behind.
The Slovenian, 33, led at the first timecheck and extended his lead over Thomas to 16 seconds halfway up the climb, before hitting a pothole and dropping his chain.
Roglic, who won the Vuelta a Espana in 2019, 2020 and 2021, will take a 14-second lead into Sunday's final, processional stage, a flat 135-km ride around Rome.
Roglic lost time and momentum while changing bikes but was able to regroup and win the brutal mountain time trial, which had 1,050 metres of climbing packed into the last 9.8km.
Joao Almeida of UAE Team Emirates finished third, 42 seconds behind Roglic.
Saturday's victory will feel like redemption for Roglic, who lost the 2020 Tour de France on the final competitive day of racing, a time trial in which he gave up his lead - and the overall race victory - to fellow Slovenian Tadej Pogacar.
Roglic cut a picture of happiness after his nerve-racking feat.
"In the end, it's not about the win, but the people, the energy, beautiful moments to experience and cherish," he said.
"One more day to go, one more focus, because I think the lap (inside Rome) is quite technical. So it's not over until it's finished. But yeah, it looks good."