IRVINE (California) (AFP) Ryan Lochte showed no sign of a groin injury that has hampered his training, surging past Tyler Clary to win the 400m medley at the US swimming championships in 4min 09.98sec on Tuesday. Lochtes time was the fastest in the world this year, improving on the 4:12.02 clocked by Japans Yuta Horihata. Christine Magnuson also notched a world-leading time on the opening night of competition, holding off a late charge by Dana Vollmer to win the 100m butterfly in 57.32. Other winners on the night included Katie Hoff in the womens 400m freestyle, Peter Vanderkaay in the mens 400m free, Ariana Kukors in the 200m individual medley and Michael Alexandrov in the 100m breaststroke. Michael Phelps took opening night of the championships off, but is slated to swim five events over the next five days in a meet that will determine the team for the Pan Pacific Championships later this month. Times from the two meetings will determine the US team for the 2011 World Championships in Shanghai. On Monday, Lochte said he was nursing a groin injury that was particularly troublesome in breaststroke. He showed no sign of it, however, as he overtook Clary on the breaststroke leg and powered home well clear of Clary (4:14.12) and Robert Margalis (4:15.62). My groin didnt hurt. I said 'If its not hurting now, lets push it, he said. He did, and at that point, Lochte said, I was like, 'Man, I think Ive got something. He said he wasnt surprised by the time, despite the recent hiccup in his preparation. Ive done the work, its just a matter of putting it together, said Lochte, who celebrated his 26th birthday on Tuesday and marked the event by wearing a pair of custom made sparkling green shoes to the starting blocks. In the womens 100m fly, Olympic silver medallist Magnuson went out strong and held off Vollmer, who settled for second in 57.45. I dont know how far ahead I was, but I knew she wasnt going to give me anything in the last 15 meters, Magnuson said. With the performance Magnuson moved ahead of Vollmer as the top performer in the event this year. She also booked her spot in the Pan Pacs that start here on August 18, when the Americans will take on Canada, Japan and Australia along with a scattering of swimmers from countries outside the traditonal Pan Pac club. I think me and Dana can really do some damage at Pan Pacs and worlds next year, Magnuson said. Kukors also came away satisfied, although her winning time of 2:10.54 was nowhere near her 200m medley world record of 2:06.15, set in winning the world title in Rome last year in one of the controverial bodysuits that have now been banned. The 2:06 and the whole worlds experience was something Ill never forget, Kukors said. But I got so much criticism for that time. Now that the suits have been banned, Kukors said, she gauges her performances not by that 2:06 but by her pre-suit best. She said her coach had spotted some errors in the race to give her something to work on until the Pan Pacs start. Alexandrov said he could also do some tinkering as continues his quest to break one minute in the 100m breaststroke. Alexandrov competed in two Olympics for his native Bulgaria but switched his sporting allegiance after the 2008 Games. His victory in the 100m breaststroke in 1:00.26 gives him a chance to represent his second home at the Pan Pacs. Hoff, who appears to be thriving after a move to the West Coast to train, won the 400m freestyle in 4:05.50 - her first national title in two years - while Vanderkaay won the mens 400m free in 3:46.88.