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The race leader seemed to be in some panic as he pulled over at the side of the road, removing helmet and jersey before running down a bank at the side of the road to relieve himself.
The Dutchman was quickly back on his bike but he was well off the back of the group containing the rest of the GC contenders.
In a controversial move Ilnur Zakarin (Katusha-Alpecin) then attacked off the front of the lead group, with Bahrain-Merida and Movistar then moving to the front to up the pace and put Dumoulin’s race lead under threat.
Dumoulin then continued his chase up the Umbrailpass as he tried to hold on to the lead of the Giro d’Italia.