The New Zealand pair looked down and out when they trailed the United States by 1.25 lengths at the 1250m mark at Laka Karapiro yesterday.
With 250m left they had reduced the gap to half a length and were quickly overhauling the Americans.
Strack (20), a member of Dunedin's North End club, and Edward (19) came home with a rush to finish third in 7min 36.73sec as the US faded to fourth in 7min 39.75sec.
The first three in the semifinals made the final.
Great Britain won the race in 7min 34.79sec with Greece second in 7min 35.40sec.
"We were stoked when we crossed the line," Strack said.
"It was the most celebration anyones seen for finishing in third place.
We were very happy.
"We saw an opportunity when the Americans faltered with 250m left and we saw the space and took it home.
"We could see them stumbling out of it and we stepped up our rating. We grew stronger and powered it to the finish."
It was a remarkable comeback by a young crew that has exceeded all expectations.
The pair were selected for the championships after winning the silver medal at the under-23 world championships in Belarus in July.
"We have taken a series of small steps and our goal is to compete at the London Olympics in two years," Strack said.
No-one would laugh at the target after considering the remarkable improvement the two have made this year.
There were two semifinals and the New Zealanders had the third-fastest time.
A podium spot tomorrow is a possibility.
"We will sit down with our coaches and readjust our race plan. We definitely want to be on the podium," Strack said.
Another New Zealand crew to make the semifinals yesterday was the women's quadruple sculls of Sarah Gray, Fiona Bourke, Genevieve Armstrong and Linda Matthews.
They finished second in their repechage in 6min 44.94sec behind Australia (6min 41.69sec).
China was third in 6min 46.38sec.
The New Zealanders went out fast with Australia and had a length on China after 750m.
China kept closing the gap in the last half of the race and was level with 200m left.
But the New Zealand crew had the endurance to hang on to advance to tomorrow's final.
It was a triumph for Bourke, a student at the University of Otago, and her Dunedin-based coach, Sonya Walker.
Bourke started rowing at the university just three years ago.
Two other New Zealand crews came close but were not able clinch a top-two spot and a finals berth.
The women's double sculls of Emma-Jane Feathery and Fiona Paterson finished third in the repechage in 7min 08.17sec behind Australia (7min 01.45sec) and Germany (7min 26.10sec).
The men's quadruple sculls of John Storey, Matthew Trott, Robert Manson and Nathan Twaddle was third in the repechage in 6min 04.88sec behind Italy (6min 01.54sec) and Great Britain (6min 02.57sec).
