O'Neill's men cruised to a comfortable victory at the Aviva Stadium on Tuesday in a performance that served as a strong response to their Euro 2016 qualifying loss to Scotland last Friday.
A double from Robbie Brady and goals Anthony Pilkington and James McClean made sure of success for Ireland despite Mikkel Diskerud's strike for USA.
Although Ireland excelled going forward, O'Neill reserved special praise for Derby County right-back Christie for an impressive maiden international display.
"I thought Cyrus Christie was excellent," O'Neill said. "He's a lot to live up to in that position with Seamus Coleman (normally there). He had a brilliant debut, really brilliant.
"I've seen a lot of him in recent months and I knew he would do well.
"He made a couple of early mistakes but he got over them but I thought he was outstanding, particularly in the second half."