Italy's Vincenzo Nibali looked primed to win gold but crashed heavily on the final descent of the 237.5km route, leaving Poland's Rafal Majka out on his own. Majka tried valiantly to hold on but with victory in sight he was caught less than two kilometres from the finish line by Van Avermaet and Fuglsang.
Van Avermaet's suffered a puncture in the early stages of the race but his powerful sprint told in the final 100 metres as he sped across the line to claim the gold medal, with Majka clinging on to third place.
Speaking of events in the final stages of the race, Van Avermaet said: “When I saw the crash I was confused about how many riders were still up the road. I was working with Fuglsang and we saw Majka. We knew it was possible. I knew I had to hang on. I am so happy for gold. Everyone said all week it was for everyone else."
Fuglsang was equally happy to claim silver. "It was a crazy race. A good race to watch," he said. "He (van Avermaet) was willing to work (in catching Majka) because he knows he's stronger than me in the sprint," he said.
A race full of sub-plots, crashes and mechanical problems proved disappointing for Tour de France champion Chris Froome, who could not join the leaders on the final climb and never featured in the medal hunt.
Froome eventually finished 12th, while his British team mate Geraint Thomas also suffered disappointment when he crashed heavily late on.
The race marked an historic day for Belgium, with Van Avermaet’s gold his country’s first at the Games since 1996. He also became Belgium’s first medallist at the event since Axel Merckx, the son of cycling great Eddy, took bronze in 2004.