The 19-year-old American set an early marker with a superb 91.20 points score, having qualified down in 10th place.

However, all the other riders came and went without passing his total, leaving Dowell as a surprise figure on top of the podium.

Russia's Irek Rizaev was also an unexpected figure on the podium in second place, while Australian Logan Martin - who topped the semi-final - was third.

Martin scored 89.6 points on his first final run, but called off his second after early errors, handing victory to Dowell.

Australia's Brandon Loupos came first in the semi-final, but landed heavily on the second jump of his first final run and immediately called it off, unhappy with the feel of his bike.

In the second run he pulled off a series of spectacular tricks - most notably a double back flip - but as he pushed in the final seconds he dismounted. 

The Australian scored 72.40 points - down in ninth place.

Another fancied competitor, Japan's Rim Nakamura, scored 86.00 points on his first run - a total booed by the crowd who felt the judges were too harsh.

He then looked to suffer a flat tyre after his first jump on round two, completely killing his run.

Nakamura continued with some big air to entertain the fans however, showing why the 17-year-old could prove a real hit at Tokyo 2020, his home Olympics.

Australia's Kyle Baldock - who qualified 24th of 24 in the first stage, but posted the fourth-best score of the semi after a brilliant ride - also called off his first run halfway through, unhappy with his performance.

His second run seemed to be much smoother but, pushing for extra points in the final 10 seconds in the final, could not produce his best in either run and finished with 62.20 points.

Australian Jake Wallwork, meanwhile, had the most bizarre ending to his competition as an attempted trick saw his bike end up in the river next to the park.

As Wallwork came down from a jump, he came off his bike, which bounced off the front wheel, over the barrier and into the water.