Czech cyclist Josef Cerny made a solo break at the end of Friday's 19th stage of the Giro d'Italia which was radically shortened after a rider protest in lashing rain forced organizers to slash more than half its distance to 124km.

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The 27-year-old Cerny covered the curtailed course like a time trial at a remarkable average speed of more than 49km an hour.

He powered through the final 23km alone to win a farewell victory for the CCC team sponsor which leaves the sport after this season.

Wilco Kelderman retained the overall lead by a handful of seconds and should be better prepared for the crucial stage 20 on Saturday after a relatively easy day in the saddle as the rider protest forced organizers to cut 134km off the original route.

Eight kilometers into the event's longest stage, the organizers neutralized the race and the riders got back on their team buses.

Australia's Adam Hansen told reporters the riders were refusing to race and wanted to find a solution.

"We weren't ready to race in those conditions, so we negotiated with the organizer to shorten the stage so that it could actually happen," said Hansen, who is about to switch from cycling to Ironman triathlons.

Race organizer Mauro Vegni saw it differently.

"I'm sorry but I did not receive a single proposition either last night or this morning," said a furious Vegni as the buses made their chaotic departure for the hastily conceived new route.

A 124km run to Morbegno embarked from Abbiategrasso with an escape group quickly forming and pulling ten minutes ahead with the peloton, which was enjoying a day of relative rest.

Team director Marc Madiot of the FDJ team was also upset by the protest.

"When you sign up for a three weeks tour you know it's going to be very tiring, if you can't accept that then change jobs," said Madiot.

Race leader Kelderman sounded happier.

"The weather was poor this morning and it was cold, it had been a hard week for our immune systems. I'm thankful the organizer shortened the stage."

Saturday's mountain stage, and an individual time-trial in Milan on Sunday, offer a testing finish to a tight battle for the overall title between Kelderman, in the pink jersey, his Australian team-mate Jai Hindley, who is 12sec behind, and Ineos breakout man Tao Geoghegan Hart in third, just 15sec off the lead.

The British rider made a bid to reduce the gap late Friday with a last gasp push for the line but failed to drop his watchful rivals.

Cerny's powerful break from 23km out proved too much for the other escapees, including time-trial specialist Victor Campenaerts, who made a late, doomed, bid to catch up.

Saturday's much-awaited run includes three ascents of the Sestrieres mountain.