Risk is part of the Olympic contest for Greg Van Avermaet who won a crash-filled Rio Games cycling road race.

Italian Tour de France winner Vincenzo Nibali crashed on a high speed descent 12 kilometers from the end and broke his collar bone.

Colombia's Sergio Henao suffered a fractured pelvis and Britain's Geraint Thomas also fell on the downhill.

Amid heat, bone-jarring cobblestones that Van Avermaet is a specialist in, and wind, only 63 of the 144 starters finished the race.

The Belgian took advantage of Nibali and Henao's falls to record his surprise gold medal.

"Everybody wanted to win, if you want to go for the win everybody takes some risk and maybe some go over the limit," said Van Avermaet, who took the tricky descent of the Vista Chinesa with a little more caution.

"The roads were ok but if you go too fast sometimes you can't take the corner.

"I was happy to stay safe ... I took a little bit of risk but not too much.

"Nowaday's you go full gas, faster and faster and you take some risk."

It was a stunning victory for the 31-year-old who is enjoying the best season of his career.

He won a Tour de France stage last month and wore the race lader's yellow jersey for three days as well.

He was also a surprise winner of the week-long Tirreno-Adriatico stage race, although that was due to the race's only mountain stage being cancelled because of bad weather.

But winning a gold medal topped the lot.

"The yellow jersey was something really special for me in the biggest race in the world," he added.

"If you love sport, you want to be the best -- in the (Olympic) Village with all these athletes, it's a special feeling."