Peter Sagan sprinted away from Silvan Dillier in the velodrome to win the Paris-Roubaix, but the race was marred by a crash that resulted in Michael Goolaerts being hospitalised.
Sagan won the Gent-Wevelgem a fortnight ago and became the first reigning world champion since Bernard Hinault in 1981 to win the Queen of the Classics on Sunday.
After making a bold attack with 55 kilometres to go, the Bora-Hansgrohe rider stuck to Dillier's wheel in a tense finish and almost inevitably surged past the Swiss surprise package to claim yet another famous victory.
READ MORE: Cyclist Michael Goolaerts taken to hospital
Niki Terpstra took third for the well-fancied Quick-Step Floors team a week after his solo Tour of Flanders triumph.
However, there was concern for the condition of Goolaerts, who was taken to hospital after crashing on a cobbled section of the 257km race.
His Veranda's Willems-Crelan team tweeted after the race: "No update on Michael Goolaerts yet. We kindly ask to refrain from speculation as we wait for an update on his situation.
"Our thoughts are with his family and friends now. Thank you for the kind messages."
There was drama when an earlier crash split the peloton in the first cobbled section, but the main contenders were able to take their place in the main pack.
Quick-Step Floors dictated the pace, but Sagan made his move and was supported by Dillier, the only rider from a nine-man break who was able to stick it out at the front.
Sagan, Dillier and Jelle Wallays (Lotto-Soudal) opened up a gap of 35 seconds to a small group, which included Terpstra, with 25km to go.
Slovakian Sagan attempted to go solo on the cobblestone sections of Carrefour de l'Arbre, but was unable to shake off the AG2R-La Mondiale man. However, he still had enough in the tank to produce a final burst in the velodrome.