Denmark's Kasper Asgreen won the Tour of Flanders cycling classic on Sunday when Mathieu Van Der Poel cracked just 50 metres from the line.

The 254km race over 19 cobbled hills ended in a two-way struggle between the pair, and as the final dash intensified the Dutchman had nothing left in the tank.

Olympic champion Greg Van Avermaet, wearing his golden helmet, came third.

It was a dramatic meltdown for defending champion Van der Poel as the Alpecin rider just seemed to give up, realising Asgreen, who was second here in 2019 too, had more strength left.

The Dane was euphoric at the line and his Belgian team Quick-Step celebrated wildly.

"It was a really hard race. We were both on the limit. It was a question of the margins at the end," said Asgreen.

"I decided to try and trust my sprint. Going into the last kilometre I got Mathieu on the front and I heard we still had more than 30 seconds," said Asgreen, knowing the following group could not catch up.

So he played the Dutchman at cat-and-mouse.

"So I decided to stay on his wheel, so I could decide when to go."

Last year, Van der Poel outsprinted his great rival Wout van Aert to win a similar two-man finish.

This time, when Asgreen sprinted, Van der Poel tried to respond but could not.

"It's an incredible team to ride for," said Asgreen, who appeared for a while to be acting as a foil for world champion Julian Alaphilippe, before the reverse proved to be the case.

The race blew open 26km from home after Asgreen's Quick-Step team was influential in catching the day's escape group that had led by 13 mins.

Van der Poel and van Aert were in the new elite group that powered ahead before Van der Poel launched a powerful assault with 12km to go. Only Asgreen was able to follow.

In other race incidents two falls and several mechanicals caused by the cobbles played havoc with even the best riders.

"It was disheartening out there," said UAE rider Matteo Trentin.

"I've been plagued by bad luck and I got a flat just as that attack took place," said the Italian who scored a second place in the Gent-Wevelgem ten days ago.

One rider Michael Schaer was thrown out of the race for throwing away a water bottle under new littering rules.

Two others were expelled in a crackdown on violent riding with Otto Vergaerde and Yevgeniy Fedorov expelled early in the race for dangerous riding after a clash of shoulders.