Viviani quickly issued a public apology to his compatriot but maintained that he felt he was unfairly blocked against the barriers in the home straight in Canale.
Cimolai opened the sprint from the bunch behind solo winner Taco van der Hoorn, moving around Viviani's lead-out man on the left before moving back over to the right. Viviani was never able to get past and settled for fourth, just behind Peter Sagan (Bora-Hansgrohe).
Beyond the line, the pair came alongside one another as their speed decreased, and Viviani appeared to elbow Cimolai's right-hand side with his left arm, albeit softly.
"I'm sorry to Cimolai for my after the finish line reaction, but when I see he do the opposite to close me on the barrier, it was really frustrating," Viviani said.
In the end, it would have been frustrating even if he had found a way past Cimolai, as Van der Hoorn foiled what appeared to be a gilt-edged opportunity.
Sagan's Bora-Hansgrohe team had set such a pace on the climbs as to weed out a number of the fastest finishers, including Caleb Ewan and stage 2 winner Tim Merlier.
"For that reason, it was a chance not to lose," Viviani said. "In the end, fourth place on the line. A lot of fatigue on the climbs for nothing."
Viviani has only won one race since joining Cofidis at the start of 2020, and is looking for his first Grand Tour stage win since the 2019 Tour de France. After his winter was disrupted by a heart problem, he has shown signs of getting up to speed at Cofidis and, after placing third the previous day in Novara, there was cause for optimism on Monday.
"We look for the next one," he said. "We are always there, so hopefully the consistency pays off."
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