Phelps fails in 100m freestyle bid
Michael Phelps prepares for his race in the men's 100m freestyle preliminaries during the 2014 Phillips 66 National Championships, at the Woollett Aquatic Center in Irvine, California, on August 6, 2014 - by Harry How
Phelps, whose record 22 Olympic medals include an astonishing 18 golds, ended a near two-year retirement in April.
But his first attempt to take his comeback to a new level by qualifying for a major international meet -- the Pan Pacific Championships later this month -- on Wednesday fell flat.
He was last at the turn and couldn't find the last-lap speed needed, settling for seventh in 49.17sec.
Nathan Adrian, the 100m free Olympic gold medalist in London, won in 48.31sec.
Ryan Lochte, whose own collection of 11 Olympic medals includes five golds, stormed to second from lane eight in 48.96.
Jimmy Feigen was third in 48.98 and Conor Dwyer was fourth in 49.06.
The top four earned berths for the Pan Pacific Championships in Australia's Gold Coast.
Results from these championships and the PanPacs will then determine the US team for the 2015 World Championships in Russia.
Phelps, who has been coy about whether his comeback is aimed at the 2016 Rio Olympics, is entered in three more events this week, just his fourth competition since coming out of retirement.
He is slated to swim the 100m butterfly on Friday -- the event he has raced the most since his return -- and the 100m backstroke and 200m individual medley on Saturday and Sunday.