O'Sullivan is in his second spell in charge of the Eagles
The United States booked a place at the 2011 World Cup in New Zealand with a 54-28 aggregate victory over Uruguay.
Eddie O'Sullivan's side won Saturday's second leg 27-6 in Florida with tries from captain Todd Clever (2), flanker Louis Stanfill and wing Kevin Swiryn.
The Eagles will play in Pool C in New Zealand, alongside Australia, Sullivan's former charges Ireland, Italy and another European qualifier.
Uruguay can still make the World Cup via the repechage.
"I was very happy with our defence, it went very well today," said O'Sullivan, whose side had scored a narrow 27-22 win in Montevideo a week before.
"We scrummaged better and stopped their rolling maul, which were the two parts of the game that we needed to improve from last week.
"I feel happy with the way we finished. Uruguay made us work for it and it should be interesting to see how they fare in repechage."
O'Sullivan also paid tribute to his players given the lack of preparation they had in the build-up to the two-legged play-off.
"It's tough to hit the ground running after not being together since July. Although we qualified, which was our ultimate goal, they were a little rusty early on," he said.
"I can't be too hard on them, though, they got the job done and you can't forget that we scored eight tries in the last two games against Uruguay."
O'Sullivan, who celebrated his 51st birthday on Saturday, is in his second spell in charge of the Eagles.
He took over from Scott Johnson in March after resigning as head coach of Ireland in March 2008 following a disappointing 2008 Six Nations campaign.