Rome, Italy (My Sportsbook) - Six world records were set on the first day of the 2009 FINA World Swim Championships in Rome and the American Olympic champion 4x100 meter men's freestyle relay team defended its title with a gold medal performance.

The group containing Michael Phelps, Ryan Lochte, Matt Grevers and Nathan Adrian finished the freestyle relay in 3:09.21, narrowly defeating the Russians (3:09.52) and French (3:09.89) to capture the gold medal. The Americans defended their world record-setting showing at the 2008 Summer Games in Beijing, where they recorded a time of 3:08.24. The United States edged France by only 0.08 in Beijing for the gold medal.

In the women's 4x100 freestyle relay, the Netherlands squad of Inge Dekker, Ranomi Kromowidjojo, Frederike Heemskerk and Magdalena Veldhuis turned in a time of 3:31.72 to shatter its own world record time of 3:33.62 set last year in Eindhoven. Germany (3:31.83) took the silver while Australia (3:33.01) placed third.

German Paul Biedermann nipped the 400-meter freestyle world record held by Australia's Ian Thorpe by one second, touching the wall with a time of 3:40.07. Thorpe's record time had stood since 2002. The silver went to Tunisia's Oussama Mellouli (3:41.11) while the bronze medal was captured by China's Zhang Lin (3:41.35).

Home crowd favorite Italian Federica Pellegrini continued an unprecedented day of racing by eclipsing her own world record in the women's 400-meter freestyle. She finished in 3:59.15 to overtake her 4:00.41 performance achieved just last month in Pescara, Italy. Great Britain's Joanne Jackson (4:00.60) took the silver while countrywoman Rebecca Adlington (4:00.79) landed the bronze medal.

In addition to the event finals, Germany's Britta Steffen eclipsed her own world record for the women's 100-meter freestyle with an opening leg of 52.22 while competing in the 4x100 freestyle relay final.

The other two world record performances came in semifinal heats, where American Ariana Kukors nailed down a time of 2:07.03 in the women's 200-meter individual medley, bettering Aussie Stephanie Rice's world record set at the Beijing Olympics by 1.42 seconds.

In the 100-meter butterfly, 15-year-old Swede Sarah Sjostrom broke former Olympic champ and Dutch swimmer Inge de Bruijn's world record of 56.61 seconds set at the 2000 Summer Games in Sydney by a mere .17 seconds (56.44).