Australian Natalya Diehm has produced the performance of her life to land a shock Olympic bronze medal in the BMX freestyle, although compatriot and gold medallist from Tokyo Logan Martin came unstuck at La Concorde in Paris.

While some of her big rivals suffered falls and botched tricks in the precarious high-flying cycling event on Wednesday, Diehm produced two superb runs on another scorching day.

"Oi! Oi! Oi!", the 26-year-old Queenslander chanted after her bronze was confirmed, while thanking her family back in Australia via video.

Diehm finished third behind Chinese winner Yawen Deng (92.60) and American silver medallist Perris Benegas (90.70), but had to watch on with fingers crossed as a series of top riders tried but failed to beat the best of her two runs, which scored 88.80 points.

Diehm had only qualified in eighth place on Tuesday but saved her best for the final, laying down an immediate marker as the second starter. 

Her excellent opening run scored over two-and-a-half points more than anything she had delivered on Tuesday.

She couldn't quite produce a better run second time around, scoring 87.70, but three of her big rivals on the final run all crashed or bailed out early, including Tokyo silver medallist American Hannah Roberts.

"I was biting my nails. I didn't want to wish that on anyone, but I wanted to podium so bad. It happened to go my way and I am so proud."

Diehm celebrated the biggest moment of her career only four years after she nearly quit the sport because of lack of funding and injury woes.

"After Tokyo, I didn't see the light at the end of the tunnel," she said.

"I just had to keep pushing forward. The one thing I knew for certain, that's not the way I wanted to go out."

Now as an Olympic medallist, she said her hope is the sport of BMX will grow off the back of her accomplishment.

"I wanted this so bad to be the first Aussie, female rider to get a medal at an Olympic Games," she said.

"I'm hoping we'll get some funding and continue to grow the sport in Australia for females, as well as males, and the kids to inspire them."

With Diehm watching on, teammate Martin struggled in the second run of the men's final.

Sitting seventh of nine after the first run, Martin needed to score over 93. He landed two tricks he had never done in a competition before, but lost speed and could not get over the ramp on his next trick.

Try as he might, Martin could not keep his feet on the pedals and slowly rode over to commiserate with Diehm, albeit with a smile on his face.

"It wasn't the day I wanted. Super disappointing to me … that I couldn't land a run," he told Channel Nine.

"Life moves on, I am OK. The good news is I do already have a gold medal at the Olympics."

AAP/ABC