CHICAGO (AP) It's Andrija Prlainovic and Serbia on the men's side, and Maggie Steffens and the U.S. for the women's tournament.
The rest is pretty murky.
The defending world water polo champions are the big favorites for the Rio Olympics, but the top challengers to each country are unclear.
''I think Serbia right now is the favorite and I think everyone else is about even,'' U.S. men's captain Tony Azevedo said. ''The Olympics is a funny tournament where it's one game a lot of times. So you could start off bad and then end strong, or start off great and end terrible. But right now Serbia is definitely the favorites I think and everyone else is just wanting to get there and stay away from them.''
Prlainovic powered Serbia to the world title last August in Russia, winning the MVP award after scoring three times in an 11-4 victory over Croatia in the final. He was named best player of January's European Championships when he collected 18 goals and 22 assists while helping Serbia to its third straight championship in the tournament, which includes many of the world's top players.
Serbia also was one of the favorites for London in 2012, but lost to Italy in the semifinals and settled for bronze. How Serbia handles the weight of expectations this time around might be its biggest unknown heading into Rio.
''That's sometimes a pressure, but they definitely deserve that because last three years they absolutely smash everyone and they won absolutely everything,'' Australia coach Elvis Fatovic said.
Steffens and the U.S. women also are on quite a roll, beating Spain 13-9 in the FINA World League Super Final on June 12. But coach Adam Krikorian said he thinks the Olympics is ''an open field.''
''I think our approach is sometimes a little different than other teams and countries,'' he said. ''We're pretty aggressive and we don't take anything that lightly so we're always in attack mode. I don't always feel like the rest of the world is in that mode. Sometimes they kind of wait for this one shot at the Olympics and to bring it. I don't think, when I look at that whole field, I don't think there's one or two teams that stand out.''
Here are a couple more things to watch in Brazil:
HEY REF: Officiating in water polo is more art than science, so adjusting quickly to how the tournaments are being called could go a long way to determining which countries makes it to the podium. ''This is very important,'' U.S. men's coach Dejan Udovicic said.
CENTER STAGE: U.S. goaltender Ashleigh Johnson is one of the most athletic players in the field, and she also helps direct the potent American attack from the cage. If the U.S. wins its second straight gold medal, she could become one of the breakout stars of Rio.
BEST MATCHUP: Serbia and Montenegro were drawn into different men's groups, increasing the possibility of a rematch of this year's compelling European final. The U.S. women have just two losses this year, both against Australia. Each country was drawn into a different group in the women's tourney.
VENUES: The first part of each tournament will be held at the Maria Lenk Aquatics Centre before moving to the Olympic Aquatics Stadium.
WORTH NOTING: The 46-year-old Udovicic coached Serbia in London, and then took over the U.S. in May 2013. He will have one of the youngest teams in the field for Rio. ''We can play with anyone,'' he said.
Jay Cohen can be reached at http://www.twitter.com/jcohenap