Thorpe swam an impressive heat time in the 200 but failed to make the final after finishing 12th of the 16 semifinalists.
He was watching from the stands on Saturday night when 20-year-old Thomas Fraser-Holmes won the 200 in 1:46.88 ahead of Kenrick Monk (1:57.16).
Thorpe's return generated enormous exposure for the Australian Olympic trials, with the South Australian Aquatic and Leisure Centre brimming to its 3,000 capacity for the night sessions which Thorpe was expected to compete in.
On Sunday morning, the venue announcer had to ask the crowd for silence at the start of Thorpe's 100. The quiet lasted only until Thorpe hit the water.
Thorpe is still a star in Australia, having won five Olympic gold medals, 11 world championships and setting 13 world records after bursting onto the scene in 1999.
"Getting knocked down from a position of immense success" Thorpe said, will be the "kick along" that his comeback needs.
"I'm pleased that when I've raced and I've struggled through racing that it's made me more determined to keep going."
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