Jai Hindley has hit the front in the Giro d'Italia, and stands just 17 kilometres away from becoming only the second Australian to win one of the three grand tour events.

A mighty mountainous stage was won by Alessandro Covi, for his first grand tour victory following a long, solo attack.

Race favourite Richard Carapaz — the 2019 champion and Olympic gold medallist in Tokyo — has led the Giro since last Saturday, but by only three seconds.

The Ineos Grenadiers cyclist cracked inside the final 3 kilometres of the penultimate stage on Saturday, and Hindley rode away to likely glory.

Hindley — who rides for Bora-Hansgrohe — will take an advantage of 1 minute, 25 seconds into the race-ending individual time trial in Verona.

If successful, Hindley will join Cadel Evans (2011 Tour de France) as the only Australian riders to win one of the three grand tour events: the Giro, the Tour de France and the Vuelta.

"We stayed patient and we really just saved ourselves until today and, actually, it was perfect.

"When I heard Carapaz was dropping the wheel I just went all out. It was an epic stage."

Hindley went into the final time trial in 2020 in the same position but the Australian finished runner-up to Tao Geoghegan Hart.

However, they were both on the same overall time and, barring an incident or disaster, Hindley should do one better on Sunday.

Mikel Landa remained third, 1:51 behind Hindley.

The 20th stage was given the maximum difficulty rating of five stars and featured three gruelling climbs: The Passo San Pellegrino, the Passo Pordoi — the race's highest point — and the final Passo Fedaia to the foot of the Marmolada glacier at the end of the 168-kilometre (104-mile) route from Belluno.

All three were top-classified ascents, with nearly 4,500 metres of climbing packed into the day.

Covi attacked on the lower slopes of the Passo Pordoi and soloed across the Cima Coppi to take the prize for crossing the highest point of the Giro first.

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He had more than 2 minutes on the remnants of the breakaway at the start of the Passo Fedaia and more than 6 minutes on the peloton.

Covi held off an attack by Domen Novak, and the Italian had time to raise his hands over his head as he crossed the line with a 32-second advantage. Giulio Ciccone was third, 0:37 behind Covi.

"I attacked from far away because I am not really a climber. I had to try and get away from everyone before the final climb," Covi said. "I rode pretty well, always full gas, push on without worrying about the legs, because they're always painful.

"It's fantastic for the team to win a stage and, particularly, this one in the mythical mountains."

AP