The victory was a huge feat for the Brazilian, who beat International Surfing Association world champion Candice Appleby of the United States. Puerto Rico's Mariecarmen Rivera took silver.

Appleby dominated most of the 5-kilometer (3-mile) distance race that zig-zagged through the main surf break at Punta Rocas beach. But she lost the heavy break shore finish when she was tumbled by a steep inside wave.

"I had a great race. I led from the start and almost to the finish but I got caught by one of those sets inside the shore break and there wasn't much I could do about it. I'd say I got a gold medal beating, that's for sure," Appleby said. "But I'm grateful to take this medal for my country. Obviously, I came for the gold, but I'm going home with a smile."

Guimaraes also beamed, her face covered in sand.

"The final was really tough. It was against Candice who was the favorite one because she's not only a great rower but a great surfer," she said.

In the final distance, Guimaraes said she saw a shortcut, and out of the corner of her eye she saw that Candice and Mariecarmen took a "more conservative" route to avoid the fall.

"I said to myself: 'I'm going to take it. ... It's all or nothing," she said.

The crowd gasped when a huge wave broke in the end. But Guimaraes made it to the shore and crossed the sandy finish line.

"I didn't even know what position I came in," she said. "I thought Candice had arrived and I was already so happy with the silver. Then I started running. My legs hurt so much. It seemed like trekking a mountain. Then I saw that she was behind. So the boldness worked today."

In the men's race, American Connor Baxter won the gold medal, paddling through the main surf break three times to end in pounding shore break.

"Beyond stoked to take the gold medal and bring it back home to my friends and family," said the Hawaii-born Baxter, who is also an ISA world gold medalist.