Michael Phelps gets ready to swim in the men's 100-meter...

Michael Phelps gets ready to swim in the men's 100-meter butterfly final at the U.S. national championships, Friday, Aug. 8, 2014, in Irvine, Calif. Phelps took second in the race. Credit: AP / Mark J. Terrill

IRVINE, Calif. -- Tom Shields upset three-time Olympic champion Michael Phelps by one one-hundredth of a second to win the 100-meter butterfly at the U.S. national championships.

Shields touched in 51.29 seconds on Friday night, tying for the second-fastest time in the world this year. Phelps was second in 51.30, losing for the second time in as many events this week.

Phelps is still likely to earn a spot on the U.S. team for the Pan Pacific Championships later this month, but he could have guaranteed himself a trip to Australia with a win in the event that he calls "my baby."

Tim Phillips was third in 51.54. Ryan Lochte finished fifth in 52.21.

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