The US National Swimming Championships opened, the first for the sport without the legendary Michael Phelps since 1998.Phelps, the winner of six medals (four gold, two silver) at the 2012 London Games, retired last year as the most decorated Olympian of all-time.The swimmers gathered Tuesday at the Indiana University Natatorium are competing for berths on the United States team for this year's World Championships in Barcelona, July 28-August 4. Do they feel any pressure to replace Phelps as the face of swimming in the US?"Absolutely not," said Missy Franklin, a 2012 Olympic standout who won five medals (four gold, one bronze) in London."I think we have so many incredible team members and so many incredible swimmers in our sport right now. It's an honor to be a part of it, and I feel like we all kind of carry that responsibility together."Franklin, best known as a backstroker, won the women's 100-meter freestyle on the opening night of the meet.The 18-year-old from Colorado came from behind to win in 53.43. Her performance was a championship record and the year's second-fastest time behind Australian Cate Campbell's 52.83."I'm so excited with that 100 time," said Franklin, who is entered in six events at nationals but is still not sure about plans for Barcelona."We'll see what happens," she said. "We won't even talk about my schedule at Worlds until I see what events I make the team in."Nathan Adrian, the Olympic men's 100m freestyle champ, repeated as the national champion in that event by finishing ahead of Jimmy Feigen in 48.10.Fourth in the race was Ryan Lochte, the winner of five medals in London. The event was the first for Lochte -- the 2012 Olympic 400-meter individual medley champ -- at this year's national meet.Another Olympic gold medalist who scored a win Tuesday was 16-year-old Katie Ledecky. Ledecky, first in the women's 800-meter freestyle at London, claimed the event here Tuesday in 8:22.41Thomas Luchsinger pulled off an upset with a first-place finish in the men's 200-meter butterfly. Luchsinger was first in 1:55.57, ahead of Tyler Clary, who was fifth in the 200 fly at last yar's Olympics. Luchsinger stroked to an early lead and withstood a late charge by Clary, whose time was 1:56.58.Cammile Adams won the women's 200 butterfly in 2:08.10. Adams took fifth in the event at the 2012 Olympics.Connor Jaeger finished first in the men's 1500 freestyle. The winning time for Jaeger, last year's Olympic sixth-placer, was 14:53.34.Caeleb Dressel lowered his own American junior record in the 100m free. The 16-year-old Dressel finished eighth with a time of 49.50.The winner of each event automatically qualify for the worlds with the rest of the team determained by a formula. A maximum of 26 men and 26 women will be selected for the USA team.