When Canadian runner Jacqueline Gareau won the Boston Marathon in 1980, she wasn't declared the winner at first.

A woman named Rosie Ruiz had crossed the finish line before her but no one could recall seeing Ruiz on the course for a large portion of the race. It turned out Ruiz had cheated. Of the 46 kilometres, Ruiz ran only about 1.5 kilometres.

Ruiz's time was 2:31:56, a few minutes quicker than Gareau's 2:34:28. Days later, when Ruiz was exposed and Gareau was declared the winner, Gareau's time would be the fastest recorded women's time until the next year's marathon.

It was Gareau's first time running in the Boston marathon.

"I was joking with friends because I wasn't sure if I was that good," Gareau told CBC Radio's The Morning Edition on Monday.

Rosie Ruiz waves to the crowd on April 22, 1980, after she was announced winner of the women's division of the Boston Marathon. Ruiz pretended to win by coming out of the crowd about one mile before the finish line. (The Associated Press)

A documentary about the history of the Boston marathon opens in Canada this week.

Gareau said someone told her she had a good chance to win the race and she joked she would look good wearing the winner's wreath.

"My goal was to break 2:35," she said.

Gareau recalled an uphill battle from the start, as an organizer said she had to start at the back or she would be disqualified.

During the race, she recalled passing a press truck and hearing Kathrine Switzer say she was in first place — but when she was nearing the finish line, she could hear someone shouting she would be the second woman to pass the finish line.

"I said 'that's not right,'" Gareau said.

Reporters then became suspicious at Ruiz's interview answers, Gareau said.

Boston: The Documentary is screening at Regina's Galaxy Cinemas in the north end of the city Monday night at 7 p.m. CST. Sunday's showing will begin at 1 p.m.