Starting the day at even par, Fox played consistent golf to be 1-under the card through 16 holes until an eagle out of the rough at the par 4, 407 meter 18th sealed him the lead with a 3-under 141 total.
"It was lucky, but it is better to be lucky than good," joked Fox at his first ever press conference.
"I was hitting out of the rough all day so I guess I knew what it was going to do, I was just trying to carry the bunker and in the air I thought that has half a chance."
"To see it go in was pretty unreal."
Already in the clubhouse at 2-under the card, Queenslander Ryan Haller and amateur Jake Higginbottom watched on as Fox stole the lead late in the afternoon.
The BMW New Zealand Open hosted by Christchurch is a premier tournament on the PGA Tour of Australasia and the most significant event 36-year-old Fox has led.
"Without doubt this is the biggest tournament I have ever led but I prefer to be leading, it's nice to be up in front - it's the best place to be," added Fox.
"It is all well and good at this stage but there is a long way to go as we are only halfway through the tournament."
Fox is a surprised leader, believing more players would have taken advantage of the easier conditions at the challenging Clearwater Golf Course.
"I was really surprised that the scores weren't lower, 4-under was leading yesterday, I kind of thought that it might have been a bit more bunch at the top with some better scores."
"I thought five or six could have been leading so it's a bit of a shock that 3-under is leading, but its good."
It was a tough finish for 19-year-old Amateur Jake Higginbottom who, after heading to the 18th a shot clear of the field, hit his tee shot into the water, finishing with a bogey.
"It was a bad swing, I slipped a little bit, but it was a bad shot," said Higginbottom who last year finished the leading amateur.
"It's great to see your name up there on the top of the leaderboard with so many good players and if I can hit it well on the weekend I think I can finish really well."
Finishing at 1-under the card are seven players including Steven Jeffress, Craig Hancock, Peter Wilson and Michael Wright as well as the the leading New Zealanders Ryan Fox, Gareth Paddison and Matthew Perry.
The Friday cut was made at 7-over par with 68 Professionals making it through to the weekend rounds.