Ruffels was attempting to become the first back-to-back winner of the prestigious United States Golf Association event in almost a decade.

Defending champion Ruffels took final opponent Rose Zhang to a second extra hole after their 36-hole final was all square and the duo made pars on the first extra hole.

But after conceding Zhang's par on the second extra hole, Ruffels, who had missed the green but hit a delicate chip to close range, missed her putt to lose the match when it cruelly lipped around the edge of the cup.

Zhang, 17, credited Ruffels for an epic duel.

"I tried to stay patient under the circumstances and getting it to a playoff was something I feel so accomplished about," Zhang said.

"The last two holes were a grind; Gabi rarely made mistakes today.

"I didn't expect anything less from her, so I tried to play my own game and turns out everything went super well.

Ruffels had won 11 straight matches before Monday's final. PHOTO: Chris Keane/USGA.

"This is insane; I think everyone dreams big but I try not to get ahead of myself.

"But now the trophy is in my hands, I really can't believe it, it's a dream come true."

Ruffels, who last year became the first Australian to win the event, was shattered at being denied the honour of back-to-back US Women's Amateur titles – a feat not achieved since LPGA Tour star Danielle Kang won the 2010 and 2011 editions.

But she had to settle for runner-up after featuring in the second-longest championship match since the US Women's Amateur started match play in 1896.

The record was 41 holes in 1966, when JoAnne Gunderson beat Marlene Stewart Streit, who both are in the World Golf Hall of Fame.

The 20-year-old is the daughter of former tennis pros Ray Ruffels and Anna-Maria Fernandez and is in her senior year of college golf at the University of Southern California.

Ruffels had won 11 straight matches before Monday's final, the longest streak to start a US Women's Amateur career since Dorothy Campbell won 13 straight from 1909 to 1911.

- Evin Priest, Australian Associated Press