In a water polo final marked by rough and aggressive play in front of both goals, Serbia showed superior firepower and defence.
Serbia's Dusan Mandic scored four times, while goalkeeper Branislav Mitrovic's impressive blocks kept Croatia out. Two goals came from Filip Filipovic, age 29 and a veteran of two past Serbian Olympic teams which each won bronze. Filipovic was elected the most valuable player of the tournament.
A Serbia team that has swept up world and regional titles since 2012 finally proved its dominance on the most prestigious stage. Filipovic said his team, known for both stellar defence and great shooting, was probably the best ever assembled in the sport.
"Let's say we want this from the whole beginning of our careers. We trained so hard, and so much we suffered," he told reporters.
Water polo is among the most popular sports in the countries of the former Yugoslavia, and before the Olympics Serbia coach Dejan Savic had said the team was under tremendous pressure to bring home the gold, telling reporters "We have won everything else, now we want this."
But early in the 12-team tournament, it looked like the unthinkable could happen to Serbia, which ran the risk of failing to pass into the knock-out rounds. The team's jittery performances began with two draws and a loss.
Serbia steadied their play in the later rounds with five straight wins on their way to the title against Croatia, which had won a gold medal in London.
Sporting rivalries have always been fierce between Serbia and Croatia, neighbouring countries that fought a war against each other in the 1990s.
Water polo matches in the region can pack stadiums with up to 25,000 fans, as happened in Belgrade at the European championships earlier this year, where Serbia won.
SERBIAN SUCCESS
With a relatively small population of less than 8 million, Serbia has had outsized success at the Rio Games.
After its men won the water polo, Serbia's women's volleyball will take on China in the gold medal match later on Saturday, following their upset of the United States.
Serbia has already captured bronze in women’s basketball, defeating France. Its men's basketball team take tournament favourites the United States in Sunday's gold medal match.
Earlier on Saturday in the bronze medal men's water polo match, Italy beat Montenegro by 12-10.
(Reporting by Joshua Schneyer; editing by Ken Ferris and Meredith Mazzilli)
