The Quick-Step Floors rider burst clear from Ireland's Sam Bennett in a chaotic finale as the rain lashed down to prevail at the end of a 155 kilometres stage in a time of 3 hours 19min 57sec.

Bennett, riding for Katusha-Alpecin, crossed in second place.

Italy and Bahrain-Merida's Niccolo Bonifazio was third across the line as all the leading riders were awarded the same time.

The day offered a partial respite for the overall contenders with three mountain stages to come later this week.

Britain and Mitchelton-Scott's Simon Yates remains 56 seconds ahead of Dutch and Team Sunweb rival Tom Dumoulin after avoiding losing too much time in yesterday's time trial.

Domenico Pozzovico of Italy and also of Bahrain-Merida lies third, 3min 11sec off the pace.

Britain's Team Sky rider and reigning Tour de France winner Chris Froome lies a further 39 seconds back in fourth.

Tomorrow will mark a tough 196 kilometres mountain stage from Abbiategrasso to Prato Nevoso.

Viviani has virtually guaranteed himself victory in the points classification with no more sprinting stages to come except for the race finale in Rome on Sunday (May 27).