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Adam Pretty, Getty Images
Rebecca Soni of the United States competes in the Women's 200m Breaststroke Heat 5 held at the National Aquatics Center on Day 5 of the Beijing 2008 Olympic Games.

BEIJING — One day after winning a silver medal in the 100-meter breaststroke, Rebecca Soni set an Olympic record in the 200-meter backstroke Wednesday night at the National Aquatics Center.

Swimming in the fifth of six qualifying heats, Soni posted a time of 2 minutes, 22.17 seconds to break the record of 2:23.37 set in 2004 by Amanda Beard.

When she finished, she looked at her time and pumped a fist in triumph.

"I didn't even know I had broken an Olympic record, it felt great," she said. "It reminded me that I am in the right place and not to stress. Just kind of need to relax and enjoy it."

The semifinals will take place Thursday morning.

The 21-year-old from Freehold, N.J., topped her own personal best this year of 2:22.60, which she swam in the U.S. Trials.

Australian Leisel Jones, who beat Soni in the 100-meter breaststroke on Tuesday by 1.56 seconds, easily advanced in her heat, winning with a time of 2:23:81. Beard swam a disappointing 2:27.70, finishing sixth in her heat and failing to advance.

Jones, who holds the world record in the event (2:20.54), didn't appear to be fazed by Soni's time.

"People have been having to swim hard in heats, having to do PBs (personal bests)," she said. "It's nice for me to know that I'm still three seconds over my best and it didn't take too much out of me."

As for the possibility of beating Jones, Soni said, "You never know what can happen. She is a great swimmer."