The 24-year-old Seto pipped his more famous rival by only 0.08sec to make a piece of history on the first day of action in the Chinese city of Hangzhou.
Italy's anti-doping agency (Nado) had demanded an eight-year ban for the 2005 and 2007 world champion.
Lochte's decision to pursue treatment follows an incident in California where police were called on Thursday morning after he tried to break into his own hotel room.
The Swede sets new World Cup mark in 50m butterfly.
The Hungarian won two gold and one bronze medals on the opening day of FINA Wolrd Cup at the Hamad Aquatic Centre.
Over 130 swimmers from 23 countries will compete in the two-day competition.
The FINA World Cup here at the Hamad Aquatic Centre from September 13 to 15.
Schooling was a rising star when he won at Incheon 2014 but, returning as one of the region's premier athletes, he swam a Games-record 51.04sec to beat China's Li Zhuhao into second place.
The 23-year-old became a national hero in the former Soviet state after a stunning victory in the 200 metres breaststroke in Rio.
Pan Pacific champ Ikee qualified second fastest for the evening's 100m butterfly final as she clocked 57.68 seconds, 13 hundredths behind China's Zhang Yufei.
The graceful 18-year-old, who lit up the recent Pan Pacific swimming championships in Tokyo, is expected to be a serious force in the 100m fly and 100m free at the 2020 Olympics in her home city.
Dressel joined forces with Phelps in the latter's final Olympics in Rio two years ago to win gold in the 4x100 metres freestyle relay.
Ledecky was 15 when she led wire-to-wire in winning the 800m free in London in a race that saw world record holder and British home hope Rebecca Adlington relegated to third.
The British swimmer stopped the clock at 57 seconds dead as he obliterated both his rivals and his own previous best mark of 57.13 seconds, which he set on the way to winning Olympic gold at Rio 2016.