Hot on the heels of his gold in the 400m individual medley a day previously at the Olympiisky Swimming Pool, Seto added the 200m IM and the 1500m freestyle titles to his collection.
He saw off the challenge of Laszlo Cseh in the 200m IM with Darian Townsend claiming third, while Anton Goncharov and Mauricio Fiol Villaneuva took second and third respectively in the 1500m free.
Townsend was able to leave Moscow with a gold though, the South African winning the 200m free ahead of Paul Biedermann and Tommasso D'Orsogna.
The Russian pair of Evgeny Korotyshkin and Nikolay Skvortsov dominated the men's 100m butterfly as American Thomas Shields settled for bronze while another Russian Stanislas Donets took victory in the 50m backstroke.
In the 200m backstroke, it was all about Japan, with Yuki Shirai claiming gold and Hayate Matsubara silver, while there were victories for George Bovell in the 50m free and Fabio Scozzoli in the 100m breaststroke.
In the women's event, Katinka Hosszu continued her domination of the series with a further three golds to add to the two won a day earlier.
The Hungarian powerhouse triumphed in the 100m and 400m IMs and the 200m butterfly to extend her lead at the top of the championship.
There were other familiar names elsewhere on top of the podiums, as world record holder Britta Steffen paced the 100m freestyle, Jessica Hardy - another world record holder - won the 50m breaststroke and Rachel Goh took the honours in the 100m back - her second gold of the event.
Inge Decker won the 50m butterfly, Rie Kaneto the 200m breast and Elena Sokolova the 400m freestyle to round off the day's results.
The FINA World Cup is a global circuit of two-day meets with cash prizes on offer for individual races.
Moscow is the fourth of eight stops on the tour with Berlin next up at the weekend.
Last year, Chad Le Clos and Therese Alshammar banked six-figure sums from the events.
- Darian Townsend