Italian Filippo Magnini rescued Andrea Benedetto who was drowning off a Sardinian beach on Sunday.
The former world champion plunged in after friends of the man shouted to sunbathers on Cala Sinzias beach, just east of Cagliari.
Magnini kept Mr Benedetto's head above water until lifeguards arrived with a raft.
"I just did what I had to," the retired sportsman said later.
Only two days before, Mr Benedetto, 45, had married his boyfriend at a ceremony in Cagliari.