The American record holder clocked 1 hour 34min 11sec - well inside the Olympic qualifying standard of 1:36:00.

San Diego's Miranda Melville captured the crowd's imagination as she also booked her Rio 2016 place in crossing the line 30 seconds later, jumping and dancing to mark her achievement.

But there was heartbreak for Eugene walker Erin Gray an hour into the race as, with a third place finish in her sights, she was disqualified for a third red flag for having both feet off the ground.

"I saw her walking off the course and my heart broke for her at that moment because the dream of 2016 was over for her," Melville said of Gray. 

"That's part of race walking, that's part of competing, that's what we do.

“We know that's part of the risk - race walking is one of the most technical events in track and field." 

On the day before the main trials got underway at the nearby stadium in HaywardField, Eugene, the walkers had their day in the sun.

Afield of 15 men and 15 women had qualified for the 20km race walking trial, which involved 19 trips back and forth down Salem's Cottage Street watched by an exuberant crowd which included a number of spectators ringing cowbells.

"I couldn't be prouder to be an Oregonian," said US men's Olympic track and field coach Vin Lananna.

"The people of Salem, as we thought they would, embraced it.

“The athletes raved about the crowd, the organization of the event and Salem being apart of the Olympic trials.

“I've said it all along - this is about Oregon, not about Eugene."

The men’s 20km title went to John Nunn, a staff sergeant in the US Army, but his time of 1:25:36 was outside the Olympic qualifying standard for the event.

Nunn will still be at Rio 2016, however, as he has already secured selection in the men’s 50km walk.

"This is the best crowd we've ever had for race walking," Nunn said. 

Michta-Coffey, meanwhile, is still considering her options about competing at Rio 2016 pending a closer scientific investigation into the mosquito-borne Zika virus which is prevalent in many parts of South America, including Brazil.

"Currently, I’m focused on being an Olympic hopeful," Michta-Coffey said on her Facebook page.

"I am drawing on all the positive energy and excitement to propel meforward in my dreams of making a second Olympic Team,.

"After I cross the line and punch my ticket to Rio I’ll let the scientist reemerge and re-analyse the current Zika status and all available info.

"Then and only then will I be able to make any further decisions regarding mine and my family’s travel plans.”