Japanese Ai Shibata emerged as the surprise winner of the women's 800m freestyle event as she took the third swimming gold for her country here Friday at the Olympic Games.

Shibata, fifth-place finisher in the 400m freestyle here, beat 400m freestyle winner Laure Manaudou to triumph in eight minutes 24.54.

"I am so surprised tonight, I thought it was a dream," said the 22-year-old Kanoya Sports Institute student.

"I was just aiming to win a medal, but winning gold makes me so happy," she said.

Manaudou, also bagging a bronze in the 100m backstroke, led the field for more than 750 meters before Shibata overtook her.

"I wasn't winning for the first 600m and when I felt that Manaudou was close, I went for it," Shibata added.

"My coach told me don't panic, don't rush and don't give up. I kept repeating this in my mind during the race," she said.

Frenchwoman Manaudou had to settle for the runner-up place in 8: 24.96 while American world silver medalist Diana Munz came third in 8:26.61.

Kosuke Kitajima clinched both men's 100m and 200m breaststroke golds for Japan here before Shibata's triumph.