There were no ill-effects of the knee injury which cut short his season back in January and threatened his participation in the tournament in New Zealand.
Reflecting on the game and what Ireland can take out of it, Ferris said: "The conditions were very slippery but we dug in well and got the win we needed.
"It was the type of tough, physical contest that we needed before we face Australia, but we felt that we left the bonus point try sitting out there.
"In the first 20 minutes I felt lethargic. I spoke to a few of the lads and they felt the same. Our legs were heavy.
"Maybe it was the travelling or nerves as that was my first World Cup game. I was nervous last night and today (Sunday).
"But as the game went on I felt more explosive and powerful. There were some big collisions which was great and the knee felt great."
It was quite a weekend for current and former Ulster players at the World Cup. Ferris turned in an impressive performance and his Ulster colleague Rory Best and former provincial team-mate Tommy Bowe accounted for Ireland's three tries.
Paul Emerick, who played for Ulster last season, claimed a late intercept try for the Americans, while Simon Danielli scored a brace of tries for Scotland and newly-appointed Ulster captain Johann Muller came off the bench in South Africa's win over Wales.
If Ireland can cut down on the errors and rediscover their best attacking form next weekend, Ferris is confident that they have the defensive strength to frustrate the Wallabies.
"Apart from the intercept try the USA didn't look like scoring a try against us. We scrambled well and our defence was solid throughout.
"If we can score one or two tries (next Saturday), hopefully our defence will keep us in the game against Australia."
Fellow back rower Jamie Heaslip was pleased to get another full game under his belt, although he admitted that the breakdown was 'a bit mental' at times.
"Off the top of my head, it was probably a combination of, at times, maybe us lacking just one extra person at the breakdown and their bringing a serious physical presence to it as well," he said.
"We played to a better shape, we probably got a lot of cobwebs out of us. I know myself, I've only had a game-and-a-half coming into this and a two-week break, so it was great to get in a shift and I know a lot of the lads will be the same as well."
With a winning World Cup debut behind him, Heaslip expects a week of thorough preparation as Ireland try to leapfrog the Tri Nations champions at the top of Pool C.
"I think we're in good shape. I haven't looked at them (Australia), I know the management probably have. We'll assess our game (on Monday), park that and then move on to Australia and see what they're all about."
Follow the Ireland team in New Zealand on www.twitter.com/irfurugby.