It was the second victory on Monday morning (AEDT) for a Dane with the surname Pedersen after Mads took Gent-Wevelgem.
The filthy conditions added to the race's intensity, the wind and rain so driving that when Pedersen (Sunweb) and Cosnefroy (AG2R La Mondiale) launched their attack, nobody was able to follow.
The 24-year-old Dane was the strongest, taking his second professional victory. Cosnefroy was left with a third podium in two weeks without lifting his arms.
Pedersen's team mate and 2018 winner Søren Kragh Andersen was a favourite for the race but a crash in the early gravel sectors ruled him out of contention.
But the outcome still went according to Sunweb's plan.
“Today went as planned from the beginning almost,” Pedersen said. “We wanted a group to go but without AG2R and FDJ so that we weren’t forced to chase alone, which is exactly what happened.
"Six guys went away and we had Martin pulling on the front so that we could sit towards the front of the peloton. Coming into the gravel sections and climbs in the finale we were in a good position. Søren was one or two positions behind me and there was a squeeze in the bunch and unfortunately Søren crashed there.
"All we could do was to stay in the front and go away with the groups. I went in a counter attack with Cosnefroy and a few others. As we caught the breakaway Cosnefroy went full gas on the attack and I managed to bridge across to him over the top of the climb and we got away. From there we went all-in to keep the chasers behind us.
"It was a dream to get a result here."
"I’ve been racing against him since U23 so I knew him and knew that if I could go with him over the hills it was a good situation. I invested a lot into pulling as we believed I could win the sprint against him if I was able to follow him on the climbs. Luckily that was exactly what happened and I’m really happy to take the win.”
While Cosnefroy could not hide his frustration nor his humility in defeat.
"I was disappointed when I crossed the line not to bring the victory to the team after they worked brilliantly for me all day long (getting us into good position on the decisive first track).
"But when your rival is stronger, there’s nothing else to do but salute him."
WATCH the full replay of Paris-Tours 2020: