With six birdies against a lone bogey the 31-year-old signed for a 5-under 67 that was good for a one-shot lead over a group of seven players including former World Number One Lee Westwood.
Teeing off the 10thin the third group of the day at the Ballyiffin Golf Club, Fox made the perfect start with a birdie at this opening hole and two more to the turn.
Another three followed on the inward half with his only blemish coming at the par-4 15th.
Fox is chasing not only a maiden European Tour victory but a place in the field for the Open Championship in two weeks’ time.
He is not yet in that field and needs to be inside the top 10 - and among the leading three players not otherwise qualified - at the end of the week.
“I'd love to be in the Open,” he said after finishing his round.
“Carnoustie is one of the best golf courses in the world I think and I'd love the chance to play there in an Open.”
He said the driver was the key to his good scoring in the opening round.
"I drove it nice,” he said. “I think I probably only hit five or six fairways but missed them in the right places and hit a lot of good drives that just ran through fairways and gave myself a lot of chance.
“As good a start as I can have, really, and hopefully three more rounds and if I can sneak in that top five like last year and get an Open spot, that would be great."
Wade Ormsby is the only other Australasian under par and inside the top 20, the South Australian T18 after an opening 2-under.
Jason Scrivener, Adam Bland, Andrew Dodt, Marcus Fraser, Brett Rumford, Scott Hend, Sam Brazel and Jason Norris all have work to do to make the cut.
Tournament host and major drawcard Rory McIlroy opened with a 2-under 70 after enduring frustration on the greens and is T18 alongside Ormsby.
“I think it’s the best I’ve hit the ball in a long time,” McIlroy said of his ball striking Thursday.
“I drove the ball very well, iron play was good I just struggled on the greens. It was either I hit good putts and just didn’t read them right or sometimes it was maybe a reaction to putts I’d hit previously, a couple of holes earlier, and it sort of just got into my head a little bit
“I holed a couple of good ones for par and holed a nice one on 12 for birdie but I’m going to need to putt a little bit better over the next three days if I’m going to have a chance.”
McIlroy’s putting has been always been streaky but has been under intense scrutiny recently though the four time major winner says he feels he is close to putting well.
“I don’t think it’s that far away,” he said. “There was a lot of putts that I felt I hit good and they were just shaving by the edges.
“I wasn’t missing by that much so a little bit of confidence, maybe see a couple go in early tomorrow, and hopefully it will be a different story.”
KIERAN PRATT SHOWS HOW TO HIT THE HIGH, SOFT BUNKER SHOT:
Want video tips delivered straight to your inbox? Subscribe to iseekgolf.com newsletters.