Proud clocked a time of 48.70 seconds for the two-length race, which was the third fastest time ever by a British swimmer and 13th quickest in the world this year.
Former Leander swimmer Calum Jarvis was second quickest in the morning heats, clocking 48.93.
Amazingly, all the finalists swam under the 50 second mark in the heats.
It meant there was frustration for Plymouth’s Levi Lucas, who missed out on the final. Lucas, who has been struggling with injury after impressing at the BUCS Championships in February, clocked 50.64 to rank 14th.
Fellow Leander swimmer Darren Lim was eighth fastest 17/18 year-old in the same event with 52.03.
Charlotte Atkinson claimed third place in the women’s open 50m butterfly time trial.
The Plymouth College pupil clocked 27.36 seconds in a race won by Loughborough’s Rachel Kelly in 26.62. Former Leander star Emma Wilkins was second in 27.01, while another former city student, Grace Vertigans, finished ninth in 27.98.
Joe Patching set a new personal best to secure third place in the men’s 50m backstroke time trial behind international stars Chris Walker-Hebborn and Liam Tancock.
Patching, who is at university in America, clocked 25.66 seconds, with Walker-Hebborn winning in 24.92 and Exeter’s world record holder Tancock clocking 25.23.
Joe Hulme was second fastest 17/18 year-old and 10th overall in the 200IM heats with 2:05.01. He will swim the junior final on Wednesday night.
Shauna Lee narrowly missed out on a place in the 400m final. She swam 4:16.48, which was just 0.12 seconds off eighth spot.
In the heats of the 200m men’s butterfly, Mount Kelly’s Alex Seymour clocked 2:12.76 and Leander’s Edward Lee 2:14.05. Former Mount Kelly pupil Cameron Brodie was the fastest qualifier in that event by more than a second, clocking 1:58.45.
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