His whole body caked in mud after 257.7 kilometres featuring 30 cobbled sectors, Colbrelli burst into tears as he collapsed on the grass of the Roubaix Velodrome after triumphing in the first rain-hit edition of the Hell of the North since 2002.
The European champion, of Team Bahrain Victorious, pipped Belgian Florian Vermeersch (Lotto Soudal) and Dutchman Mathieu van der Poel (Alpecin-Fenix), who were second and third respectively.
Van der Poel, one of the pre-race favourites, came up just short after doing most of the work in a small group chasing Italian Gianni Moscon, who seemed to be heading to victory before a puncture and late crash ruined his chances.
Moscon (Ineos-Grenadiers) eventually finished fourth, 44 seconds off the pace, leaving his compatriot Colbrelli to become the first Italian to win here since Andrea Taffi in 1999.
“It’s unbelievable. My first Paris-Roubaix and I’m very happy. It was a legendary Paris-Roubaix, no? With the rain and the start. I attacked with 90 kilometres to go after Arenberg and in the final I followed van der Poel. I had a super sprint and I’m very happy for this victory,” said Colbrelli.
"I followed only Van der Poel in the finale and in the end I had a super sprint. I was at the limit in the finale.
It was super difficult because I had to pay attention to the crashes from the first sectors and then there’s always the stress to be in position on the cobbles. This year is my year, I’m very happy."
Van der Poel, who was also making his debut on the Paris-Roubaix in the first edition since April 2019 after the COVID-19 pandemic prompted organisers to put off the event, matched his father Adrie's podium finish from 1986.
Countless crashes marred the race with triple world champion Peter Sagan hitting the deck and Swiss Stefan Kueng going down three times.