Trailing 5-3 midway through the second quarter, the Americans cranked up the defence and shut down the Romania attack while scoring four unanswered goals of their own — two of them from Bailey — to take control of the match.
"It's the games like this when you start slow that you learn the most," said U.S. captain Tony Azevedo. "Romania came out great, came out hitting and punching, and the referees let it go and our team responded well toward the second half. That's why we trained for seven months together, to be in better shape than everyone else, and we wore them out toward the end and we closed the deal."
The win puts the U.S., which took silver four years ago in Beijing, level with gold medal-favourite Serbia atop Group B with four point after two matches.
And with Serbia and three-time defending champion Hungary still ahead for the Americans in the group stage, the win over Romania was key to easing the way for the U.S. into the quarterfinals.
Bailey, who at 36 is playing in his fourth Olympics, said the U.S. knew that Romania wouldn't be an easy opponent, despite the fact that the country is playing in its first games since 1996 in Atlanta.
"Romania's a tough team. These guys came into the Olympics knowing that they had to beat us if they wanted to get into the top four in our group," he said. "They came out to play and kind of put it on us there in the first half, and we just hung in there and kind of wore them down in the second half."
The 12-team field in men's water polo is broken down into two groups of six for the preliminary stage, and the top four teams from each group advance to the knockout round.
The U.S. next plays Britain, which lost to Serbia 21-7, on Thursday.
Ryan Lucas can be reached on twitter at www.twitter.com/relucasz