Vanja Udovicic scored three goals and Filip Filipovic chipped in with two more to give Serbia an 11-6 win over the United States on Saturday in men's Olympic water polo.
It was the first loss for a U.S. team that is packed with Bay Area talent.
The win lifted Serbia into first place in Group B with seven points and secured a spot in the quarterfinals. It can wrap up the group's top seed for the knockout stage by beating Romania in its last preliminary-round game on Monday.
The U.S., which had already guaranteed itself a spot in the quarterfinals, is one point behind the Serbs, and plays three-time defending champion Hungary in its last group game.
"Serbia's a great team, they're very good. Clearly right now they're the favorites," U.S. captain and Stanford graduate Tony Azevedo said.
He said the Americans did not play to their strengths against Serbia.
"We're known for not giving up counter goals, set goals, and putting away our six-on-five, and we did the opposite today — we gave up six counter attack goals — that's unheard of," Azevedo said.
Azevedo is joined by other Bay Area players including Layne Beaubien, Peter Hudnut, John Mann and Peter Varellas.
The Americans were the runners-up four years ago in Beijing.
The men's field is broken into two groups of six teams. The top four from each group advance to the quarterfinals.
On the other side of the bracket, Croatia stayed unbeaten and secured the top spot in Group A with its 11-6 win over Australia.
"Our form is improving. That's the most important because no matter who comes from the other group it will be a very, very hard quarterfinal," Croatia captain Miho Boskovic said.
Maro Jokovic led the way with three goals for Croatia, which won the FINA World League title last month.
While the Croats said locking up the No. 1 seed gives them a small boost, they stressed that it means little practically because of the quality of the teams in Group B.
"Maybe psychologically it helps, but the opponents in the other group are really strong so it doesn't really matter," Sukno said.
Two other teams in Group A — Spain and Italy — also wrapped up spots in the quarterfinals.
Filipe Perrone Rocha scored twice to push Spain past Greece 11-9, while four players netted two goals for Italy in a 9-6 win over Kazakhstan.
Spain plays Italy in their final group game Monday, and the winner will earn the No. 2 seed out of the group for the quarterfinals. Spain can also secure the second spot with a draw.
Greece, meanwhile, has just two points from four games, but can still advance by winning its final preliminary-stage game Monday against Australia.