Natalie Coughlin swims during her heat in the women's 200m individual medley at the U.S. Olympic Swimming Trials in Omaha, Nebraska July 1, 2008. (Xinhua/Reuters Photo) Photo Gallery>>>

    BEIJING, July 2 -- Natalie Coughlin and Hayley McGregory blitzed to back-to-back world records and Katie Hoff secured her second Olympic berth at the U.S. swimming trials in Omaha, Nebraska, on Monday.

    Just two days into the eight-day competition, four world records have fallen as American swimmers engage in a cut-throat battle for places in the Beijing Olympic team.

    With only the top two finishers in each event qualifying, the competition has been fierce.

    Even though McGregory and Coughlin posted world records in the 100 metres backstroke preliminaries, that was only good enough to take them as far as the final.

Katie Hoff leaves the starting block during her heat in the women's 200m freestyle at the U.S. Olympic Swimming Trials in Omaha, Nebraska July 1, 2008. (Xinhua/Reuters Photo) Photo Gallery>>>

   Hoff, however, coming off a world record in the 400m medley on Sunday, qualified for her second Olympic event by touching first in the 400m freestyle with the third best time this year of four minutes, 2.32 seconds.

    Day 2 got off to an electric start when McGregory powered home in a time of 59.15 in the heats to steal Coughlin's world record. But McGregory's reign lasted only as long as it took Coughlin to complete her heat - the 25-year-old storming to the wall in 59.03 to retake her record.

    Neither of them were able to better that time in the semis but set up a mouth-watering showdown in the final.

    "It just felt different, my body was a little tight," McGregory told reporters. "Natalie and I have different strengths and I don't get to swim against her very often."

    Michael Phelps was left to celebrate his 23rd birthday quietly by qualifying for the 200 metres freestyle final.

Michael Phelps heads into the water for his heat in the men's 200m butterfly at the U.S. Olympic Swimming Trials in Omaha, Nebraska July 1, 2008.(Xinhua/Reuters Photo) Photo Gallery>>>

    A day after demolishing his own world record in the 400 medley, Phelps was back in the pool and cruising to easy wins in his preliminary and semifinal heats.

    Ryan Lochte, who chased Phelps to his 400 individual medley record, set up another showdown with the six-times Olympic gold medallist in the 200m final after clocking the year's best time of 1:45.61 to win his semifinal.

    "I'm happy with it," said Phelps, who is targeting Mark Spitz's record of seven gold medals at a single Summer Olympics. "I'm getting a good feel for my stroke."

    World record holder Brendan Hansen set the stage for an Olympic showdown with archrival Kosuke Kitajima of Japan by touching first in the 100m breaststroke in 59.93.

    "I didn't break my world record but having that Olympic berth solidified feels very good," Hansen said. "I think for everyone of us this is the toughest part of the summer, trying to make the Olympic team."

    In the 100m butterfly final, Christine Magnuson came home first in 58.11 ahead of Elaine Breeden and both women qualified for their first Olympics.

    (Source: Shanghai Daily/Agencies)