Ryan Fox was surprised on Friday to find himself leading the Irish Open after the opening round, despite his impressive form this season.

Fox had eight birdies, including seven in his last 11 holes, in a flawless 8-under 64 at Mount Juliet. He has a one-shot lead over Frederic Lacroix, Jorge Campillo, Fabrizio Zanotti and Marcel Schneider.

Fox, who lost a playoff for the 2018 Irish Open to Scotland's Russell Knox, won the Ras Al Khaimah Classic in February, finished runner-up in the Soudal Open and Dutch Open and was third in the BMW International on Monday.

"I'm more surprised, to be honest, than anything else," the 56th-ranked Fox said. "I've been fighting it on the range the last couple of days and a 64 certainly didn't look likely early in the round.

"I made a couple of birdies but I was scrapping away and hit a great wedge on my eighth hole (the 17th) and made a few putts as well. So just one of those days that shows how important patience is in a round of golf."

Fox, who is arguably in career-best form, says he can't pinpoint one specific thing that has contributed to his recent success.

"It's probably a multitude of things to be honest," Fox told NZME following his round.

"I'm really happy with the team I've got around me: my caddy, both coaches I'm working with, psychologist, physio, all of those. Everyone's on the same page and everything's been working really well on the golf course.

"Off the golf course, I'm just a lot happier with where things are at than what they've been in the last couple of years and obviously there's a few factors that were out of my control.

"There's probably been a few sportspeople over the years that have been able to perform at the highest level with whatever has been going on off the field, but that's probably not me."

Three-time major winner Padraig Harrington shot a 2-under 70 just days after his victory in the US Senior Open, while 2019 Open champion Shane Lowry had to settle for a 71.

"It's a pity with the finish," said Harrington, who bogeyed two of his last three holes. "It's just a part of the game, isn't it?"

- additional reporting by Matt Brown, NZME.