LONDON — As Australia’s Sally Pearson sailed over hurdle after hurdle Tuesday, a crowd of 80,000 at Olympic Stadium erupted in a roar, but she said she could not hear a thing.

It was like she was racing the 100-meter hurdles by herself, churning her legs in silence as the finish line grew near. So when she turned to see Dawn Harper of the United States next to her as they crossed the finish, it startled her.

“Wow, she’s really close,” Pearson recalled thinking. “Did she come first?”

Deep down, though, Pearson said she knew the gold medal was hers. And she was right. She saw her name pop up on the scoreboard and collapsed to the track that was moist with rain, sobbed and let the moment sink in.

“I’ve got every title now that I’ve ever wanted to win,” she said.

Pearson set an Olympic record with her time of 12.35 seconds, and Harper was right behind her in 12.37 to win the silver medal. Kellie Wells of the United States, who finished in 12.48 seconds, won the bronze. Lolo Jones, also of the United States, was fourth.