David Davies put years of fatigue problems aside to reach his third Olympics after booking a spot in the 1,500 metres freestyle alongside Daniel Fogg in the final event of the trials at the Aquatics Centre.
Fogg became only the third Briton after Davies and Graeme Smith to go inside the 15-minute mark when he won in 14 minutes 55.30 seconds.
City of Cardiff swimmer Davies was 5.43secs adrift with the former training partners both inside the qualifying time.
It also means the pair will battle it out for one place in the open water competition in the Serpentine at the final qualification event in Portugal in June.
Davies, who won bronze in the 1,500m in his first Olympics in 2004, was dogged by exhaustion since 2009 and a year later he returned to former coach Dave Haller from Kevin Renshaw at Loughborough, under whom he won 2008 Olympic open water silver.
Fran Halsall equalled Inge de Bruijn's textile world record as she booked her third slot with victory in the 50m freestyle.
The 21-year-old blasted off the blocks and there was soon daylight between her and the rest of the field.
Halsall, fourth in this event in Shanghai, touched in 24.13, the same as De Bruijn clocked at the Sydney Olympics in 12 years ago.
It was just two hundredths of a second off her own British record set in a 100% polyurethane suit in 2009.
Amy Smith, of Loughborough University, also went under 25 seconds for the first time, her effort of 24.80 ensuring she would join Halsall.
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