Greg Van Avermaet (BMC Racing) stood on the podium and accepted the cobble trophy as the race winner. Zdenek Stybar (Quick-Step Floors) placed second and Sebastian Langeveld (Cannondale-Drapac) third. Sagan finished 38th at 5-12 minutes.
Sagan showered, exited the Bora-Hansgrohe team bus, kissed his wife and hugged his dad. He walked to the fans to sign their hats and shirts, and turned back to the waiting journalists with a shrug of his shoulder.
"I had two flats..." he said.
"I'd spent a lot of energy to go on the attack, because it's not easy for me to get away when they see me move. I managed to do it twice but I was slowed by punctures.
"It was a bit of an unlucky day for me but then I ran out of energy to be up front in the action."
Sagan lit up the Spring Classics in his rainbow jersey, however. He won only Kuurne-Brussels-Kuurne, but he attacked on the Poggio to blow Milan-San Remo apart and drove through the Oude Kwaremont to create the hottest YouTube clip when he snagged a fan's jacket with his handlebars and crashed.
"An unlucky campaign? I lost Milan-San Remo. At the Tour of Flanders, I made a mistake and then today I was unlucky."
Philippe Gilbert (Quick-Step Floors) caught Sagan out with an early attack in the Tour of Flanders. This time, Sagan attacked with 77.7 kilometres remaining and formed a group team-mate Maciej Bodnar, Daniel Oss (BMC Racing) and Jasper Stuyven (Trek-Segafredo).
A puncture took its toll that time and again another time, at 32 kilometres to race when he sat with eventual winner Van Avermaet and runner-up Stybar.
"It's a hard day when you work hard to get a result, and you don't have the best of luck," sports director and coach Patxi Vila said.
"You have to always think anything can happy, you just have to keep fighting. Greg Van Avermaet was in the crash and he came back and finally he won.
"The team worked well, Peter was in the right moment and doing the right things."
He said that his hip did not bother him after his Oude Kwaremont fall last Sunday.
"I'm happy with my form, but not with the results. I can't be happy with the results I got," said Sagan.
He placed second in Omloop Het Nieuwsblad, won Kuurne-Brussels-Kuurne, second in Milan-San Remo, 108th in the E3 Harelbeke, third in Ghent-Wevelgem and 27th in the Tour of Flanders.
Some critics think that Paris-Roubaix could have been a race too much for Sagan. Before, team Liquigas/Cannondale would have him skip Paris-Roubaix and maybe race the Amstel Gold Race a week later.
"You're always tired after Paris-Roubaix and today I'm very tired," Sagan added.
"But the season continues. I'll take a bit of a break now and then I'll get going again at the Tour of California. Then I'll have important races like the Tour de Suisse and the Tour de France."
Thank you for reading 20 articles this month* Join now for unlimited access
Enjoy your first month for just £1 / $1 / €1
*Read 5 free articles per month without a subscription
Join now for unlimited access
Try first month for just £1 / $1 / €1