Phelps, on the comeback trail after retiring, finished a distant seventh in the 100m free final won by reigning Olympic champion Nathan Adrian at the US Swimming Championships, unable to recover after misjudging the turn.
"It just kind of stinks that I missed the first wall, but it's a part of racing," said Phelps, 29, who needed a top-four finish to book a spot in US team for the Pan Pacific Championships August 21-25 in Gold Coast, Australia.
Phelps, an 18-time Olympic champion, was especially frustrated because he thought he had warmed up well but once he was in the turn he knew that he wouldn't have enough momentum coming off the wall to mount any second-lap challenge.
"I knew there was very little chance that I was going to run anybody down," he said.
Watching the race, coach Bob Bowman knew it too.
"From a dead stop, it just doesn't happen in a race like that," said Bowman.
Adrian won in 48.31sec. Ryan Lochte, whose own collection of 11 Olympic medals includes five gold medals, stormed to second from lane eight in 48.96.
Jimmy Feigen was third in 48.98 and Conor Dwyer was fourth in 49.06.
"He said he missed the turn," Lochte said of his longtime rival Phelps.

"I saw it, because when I flipped I looked under water and saw him. Things happen. He is going to fix it and make sure it never happens again,” he added.

Results from these championships and the PanPacs will determine US team for the 2015 World Championships in Russia, a key meet in the build-up to the 2016 Olympics.
Phelps, who has been coy about whether his comeback is aimed at Rio, is entered in three more events this week, just his fourth competition since he ended a near 20-month retirement in April.
He was already looking forward to Friday's 100m butterfly -- the event he has raced the most since his return.
"I'm just trying to get a spot on the team and go from there," Phelps said.

"I am ready to have a day off and get ready for the 100m fly,” he added.
Phelps is also slated to swim the 100m backstroke on Saturday and the 200m individual medley on Sunday.
If Phelps does make the PanPacs team in another event, the rules for the meet mean he could swim at least the heats of the 100m free there, and would be eligible to swim the
4x100m free relay.
Although the 100m free was never one of Phelps' signature Olympic events, the 4x100 free relay has figured in his epic Games campaigns.
"He puts himself on that team, he can certainly be a candidate for the relay," Adrian said.

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