Van Summeren broke away with 13km of the race left
Belgian rider Johan van Summeren won his first Paris-Roubaix Classic after breaking away in the closing stages and holding on for an unexpected victory.
Van Summeren completed the 258km-long course in six hours seven minutes and 28 seconds.
He finished 19 seconds ahead of two-time winner Fabian Cancellara and Dutchman Maarten Tjallingii.
"Once I got up in the front group, I felt I could win," said Van Summeren. "It's wonderful."
The race, famed for its treacherous cobblestones sections, included several spectacular crashes, with a number of riders involved including British duo Roger Hammond and Geraint Thomas.
Team Sky's Ian Stannard was the leading Briton in 36th - 4.46 behind van Summeren while Bradley Wiggins, who finished well down in 90th, almost 14 minutes behind the winner, needed stitches to his knee and Mark Cavendish also failed to finish.
Wiggins forged an early breakaway, where he was joined by Italian riders Marco Bandiera and Mirko Selvaggi in a bid to gain early ground in order to better help his Sky teammate Juan Antonio Flecha of Spain later on in the race. But Flecha, third last year, finished down in ninth place - one spot ahead of team-mate Mathew Hayman.
Three riders joined the front three to form a six-man breakaway which led by 35 seconds after 50km.
They were caught soon before the first cobblestone section. But Russian rider Vladimir Gusev and Frenchman Renaud Dion crashed before they could even reach it, and shortly after the first cobbles a new group of 10 formed a breakaway.
About 80km from the end, former three-time winner Tom Boonen suffered a puncture which although repaired, saw him lose considerable time.
His luck got worse when he was one of several riders to crash on the cobbles after a Rabobank rider tumbled sideways off his saddle and brought others down with him.
Also among the fallers were Frenchman Sylvain Chavanel, Italy's Filippo Pozzato, the runner-up in 2009, and Slovakia's Peter Sagan.
Van Summeren tried his luck and broke away with 13km left and was able to hold on for a famous victory.
Johan van Summeren (Bel/Garmin) 6hrs 07mins 28secs
Fabian Cancellara (Swi/Leopard) +19 seconds
Maarten Tjallingii (Ned/Rabobank) same time
Gregory Rast (Swi/RadioShack) same time
Lars Bak (Den/HTC-Highroad) +21 seconds
Alessandro Ballan (Ita/BMC Racing) +36 seconds
Bernhard Eisel (Aut/HTC - Highroad) +47 seconds
Thor Hushovd (Nor/Garmin) same time
Juan Antonio Flecha (Spn/Team Sky) same time
Mathew Hayman (Aus/Team Sky) same time