New York teenager Magnus Sheffield broke away for a solo triumph at cycling's Brabantse Pijl one-day classic on Wednesday while world champion Julian Alaphilippe crashed after his own team car caused a domino effect of falls. 

Sheffield, 19, was part of an eight-rider group who had dropped the rest of the field and he made his move two kilometres from the Overijse finish line.

The Ineos Grenadiers rider had two teammates in the small, pursuing group who refused to chase leaving the rookie to ease over the final 100m and slowly raise his arms in celebration at an unexpected win.

"It's unbelievable. When I broke off the front I never expected to win," Sheffield said.

"These races are not for the mentally soft and with this awful weather, I mean it was kind of gritty and cold out there," he said.

His win came thanks to a strong Ineos performance with teammates Tom Pidcock and Ben Turner.

"I just felt unbelievable when I found myself off the front in the last kilometers, and I really didn't expect to hold on," he said.

"I just followed a move with Wellens, and he swung off, and I found myself alone, and I kept going to force the others to chase. Everyone was looking at each other, and I just went full gas and put it in the biggest gear, and tried to make it to the finish," Sheffield said. "To be able to win a one-day, especially in these semi-classics is just unbelievable."

Sheffield's winning break followed closely on the heels of Alaphilippe's dramatic fall after the Frenchman's own team car clipped another rider causing a quick succession of other falls.

After dusting himself down, Alaphilippe eventually returned to the saddle of his bike.

This is a second win for Ineos in less than a week after Poland's Michal Kwiatkowski won the Amstel Gold classic on Sunday.

In that race, French AG2R rider Benoit Cosnefroy thought he had won only to be classified second after a photo-finish.

He was second again on Wednesday.