In dramatic scenes unseen on the Tour de France in recent years, Italy's Nibali (Astana) took more than two and a half minutes from Spaniard Alberto Contador (Tinkoff-Saxo) after British defending champion Froome (Team Sky) withdrew from the race before the first of seven cobbled sections.
Nibali, the Italian national champion, took third place in the 155.5km stage from Ypres to Arenberg-La Porte Hainaut, crossing the line alongside team-mate Jakob Fuglsang nineteen seconds behind Belkin's Boom.
The sight of cobbles specialists Peter Sagan (Cannondale) and Fabian Cancellara (Trek Factory Racing) battling it out for fourth place one minute in arrears emphasised the colossal achievement of Nibali, a rider not renowned for his prowess on the pavé.
Nibali is two seconds clear of Fuglsang in the general classification with Sagan now third at 44 seconds. While Lotto Belisol's Jurgen van den Broeck (+1:45), Garmin-Sharp's Andrew Talansky (+2:05) and Movistar's Alejandro Valverde (+2:11) finished strongly in a chasing group; double Tour winner Contador struggled on the cobbles to drop out of the top ten: he lies in 19th place, 2:37 down on Nibali.
Boom made his decisive move in the final cobbled sector six kilometres from the finish, the Dutchman riding away from team-mates Nibali and Fuglsang to secure the biggest win of his career to date.
"It's a dream to win a stage on the Tour de France - especially on the cobbles and in this kind of weather," said 28-year-old Boom, who this week was tipped to join Sky in the wake of Belkin ending their sponsorship agreement with his Dutch team.
How Sky could have done with Boom's services on a miserable day for Sir Dave Brailsford's outfit. Things looked ominous from the outset when Froome - raw and tender from his crash a day previously - skidded on the wet roads and hit the deck after just 35km of the stage.
When team-mate Vasil Kiryienka skidded on a roundabout with 70km remaining Froome managed to avoid the Belorussian's sprawling body - only to fall himself moments later. Visibly distressed and in considerable pain, the defending champion could take no more and hobbled into the Sky team car just as his previous rivals for the maillot jaune entered the first cobbled section of Gruson.
Heavy rain and flooding had caused the Tour organisers to cancel two of the scheduled nine cobbled sectors - and although Froome's accidents were not directly caused by the cobbles, the psychological effect of their impending arrival must have played a huge part in his demise.
The pace was extremely high entering the Gruson section - and Froome was not the only rider to suffer the consequences. Valverde crashed and had to chase back on with his Movistar team-mates, while a trail of devastation included crashes for Sky's new number one - the Australian Richie Porte - as well as Talansky, van den Broeck and even Cancellara.
NINE-MAN BREAK: Lieuwe Westra (Astana), Tony Martin (Omega Pharma-Quick Step), Tony Gallopin (Lotto-Belisol), Marcus Burghardt (BMC), Rein Taaramae (Cofidis), Simon Clarke (Orica-GreenEdge), Mat Hayman (Orica-GreenEdge), Janier Acevedo (Garmin-Sharp) and Samuel Dumoulin (Ag2R-La Mondiale) had formed the day's break shortly after the start in Belgium.
After building up a maximum lead of just over three minutes, the break fractured when a crash ended Acevedo's chances and saw both Martin and Dumoulin momentarily dropped as the peloton closed in. One by one, the break lost bodies as the cobbles took their toll - a select core of Gallopin, Westra and Hayman caught by Belkin duo Boom and Sep Vanmarcke with around 30km remaining.
The crashes continued to thwart the entire peloton: Heinrich Haussler (IAM) twice went down, Talansky collided with a spectator, Lars Bak (Lotto Belisol) went head over heels into a ditch and one Movistar rider sent a fan sprawling into a puddle beside the road. These were just the tip of the iceberg on a day of drama, pain and suffering.
Second in Paris-Roubaix in 2012, Vanmarcke's composure on these gritty tracks of northern France really showed - until his bid for glory was derailed with an untimely puncture 24km from the finish.
At this stage, Contador has been well dropped, while Porte and Sky team-mate Geraint Thomas rode in a chasing group with Talansky and van den Broeck. Porte would eventually cross the line with his shorts torn to expose a nasty gash on his thigh, the Tasmanian now Sky's best-placed rider on GC, 1:54 down in eighth place.
RIDE OF THE DAY: Take nothing away from Lars Boom - his victory was sensational - but the Dutchman was born and bred for this kind of racing. Vincenzo Nibali has never even raced Paris-Roubaix before and yet he took to the cobbles like the proverbial fish in water - making a mockery of specialists Sagan and Cancellara, who couldn't keep up with the searing accelerations of the yellow jersey.
DAY TO FORGET: Chris Froome - although he will not forget it in a while. Everyone had stage five down as the one that would pose the defending champion the biggest questions - and in the end, it was not the cobbles that did for him, but a series of crashes on wet roads as the race nervously approached the first sector.
COMING UP: Marcel Kittel would be a shoo-in to pick up his fourth win of the race in the largely flat 194km ride from Arras to Reims. But the German sprinter from Giant-Shimano was one of many riders to hit the deck - as was compatriot Andre Greipel (Lotto Belisol), Norway's Alexander Kristoff (Katusha) and Frenchman Arnaud Demare (FDJ) - on the cobbles so perhaps we will see some of the other sprinters contest the victory. Perhaps Peter Sagan can break his duck?
PLAT DU JOUR: Reims is the centre of Champagne production and so the winner on Thursday will be able to pop a cork or two. To soak it up, local pork terrine braised in salted brine and set in warm gelatine would go down a treat - followed by some of the famous local pink vanilla biscuits.
- Sports & Recreation
- Alberto Contador
- Peter Sagan
- Tour de France
- Fabian Cancellara
- Jakob Fuglsang
- Andrew Talansky
- Lotto Belisol
- Chris Froome
- Jurgen van den Broeck