"It's giving me a bit of grief," said Walker. "But I was definitely improving this weekend and quite happy with my progress. I was first to the second corner in the quarter and semifinal which is encouraging. That's in line with where things are at with my training.
"For me this is a minor setback and nothing I can't handle."
Walker qualified seventh in Saturday's time trials, and finished top of her three qualifying motos yesterday. She finished second to Beijing silver medallist Laetitia LeCorguille (France) in the opening two heats but grabbed her first win of the season with an impressive effort in the final moto.
The Rotorua rider, who now lives in Cambridge, was fast out of the gate in the semifinal but cruised home in third behind LeCorguille and American Arielle Martin.
Walker jumped strongly in the final and was second in the second straight before crashing when she became squeezed for room between LeCorguille and Martin, and was then hit by a following rider.
Australian Caroline Buchanan came from behind to pip Magalie Pottier (France) on the line to win the women's final.
Willers, fourth in the opening round of the Supercross World Cup in California last month, had solid qualifying motos yesterday, finishing second behind Willoughby who won all three heats. The Kiwi had two seconds and a fourth to be second qualifier.
The California-based New Zealander jumped well in his quarterfinal, just headed by Willloughby into the first corner.
Willers pushed hard down the second straight but was airborne with nowhere to go when the Australian moved lines going into the second corner. He hit the back of Willoughby and came down, with American Barry Nobles crashing into him from behind.
"Sam just got squirrelly going into the corner and I could not change line because I was already in the air and I ran into him. It's disappointing because my form is definitely improving and on track.
"I guess that will teach me for not being first into that first corner."
American Connor Fields continues his excellent form to hold off Willoughby by 2/1000ths of a second in the men's final.