Midway through the second women's 5000m heat the pack bunched up and New Zealand runner Nikki Hamblin checked her stride.

Behind her American runner Abbey D'Agostino clipped her legs and they both stumbled.

D'Agostino was quicker to her feet at first. Stuck on the track, Hamblin was stunned. "When I went down it was like, 'what's happening? Why am I on the ground?' " she said.

And suddenly there's this hand on my shoulder, like 'get up, get up, we have to finish this!'

"I'm so grateful for Abbey for doing that for me. That girl is the Olympic spirit right there.

"I've never met her before. Isn't that so amazing?"

But once both were upright, it was apparent that D'Agostino was the worse off of the pair and she went down again. She urged Hamblin to go on, but in a moment reminiscent of John Landy's immortalised hand to fellow Australian Ron Clarke in 1956, the Kiwi waited for the American before setting off again.

"Someone had to go help her," Hamblin said.

"And if I could even give her one per cent back of what she gave me when she helped me get off the track, that would be amazing.

"She was like, 'go on, go on, I don't know if I can run, keep going, keep going!' "

"She was saying, 'I can't put weight on my knee.' It was buckling."

But go on D'Agostino did. Clearly pained, she shuffle-limped on, drawing rapturous applause from those in attendance at the Estadio Olimpico.

"She ran 4½ laps barely being able to run," Hamblin said in awe of the woman with whom she will be forever tied.

Both of them knew their chances in the race were shot but ran on to finish. They embraced at the finish line and a wheelchair was brought out for D'Agostino who could not run a step more. The pair were the last over the line - Hamblin finished in 16.43.61, D'Agostino in 17.10.02.

Saddened by the American's fate, Hamblin said the 24-year-old had a bright future.

"Being such a good human being, she's going to go so far."

Moreover Hamblin - who had suffered a similar fall at the World Championships - could see the bigger picture.

"You come into an Olympic Games and everyone wants to win, everyone wants to medal.

"But really as disappointing as this experience is there is so much more to this than a medal.

"When someone asks me what happened in Rio in 20 years time, that's my story."

In the final of the 1500m at the 1956 Australian National Championships, Landy famously stopped and doubled-back to check on fellow runner Clarke after another runner clipped Clarke's heel, causing him to fall in the third lap of the race.

Incredibly, in the final two laps Landy made up a large deficit to win the race, and the moment is considered one of the greatest moments in Australian sporting history.