Brown signed for an 11-under 59 and matched the official course record held by Auckland professional Richard Lee.
The former European Tour pro, who opened with a two-under 68, climbed to 13-under at the halfway stage of the $40,000 Carrus Open on the Charles Tour to earn a three shot lead from Fiji professional Vikrant Chandra (66).
Lee (68) and Tasman amateur Ryan Chisnall (65) are in a share of third place but the talk of the clubhouse was the performance of Brown.
The Shandon golfer was high-fived and congratulated all the way back to the clubhouse as the 50 spectators who watched his round knew that they had witnessed something remarkable.
The renowned ball striker played his final 10 holes in a world-class 10-under.
"It is an awesome feeling," said Brown. "I was saying yesterday how many days with golf you have when you walk off the course frustrated or that you have left a few out there. So to have the feeling where you have scored as well as you possibly can on every hole is a unique feeling and an amazing feeling. Especially to do it around here where I have a lot of friends, it is really special."
The New Zealand Open runner-up made the turn in one under par before going on a phenomenal run where he made seven birdies and an eagle to complete the best nine holes of his life.
Brown hit his approaches to within 4m on his first four holes of his back nine and then to 6m on the fifth and made all the birdie putts in nonchalant fashion.
He made an eagle from 10m on the fringe of the par five 6th and then delivered probably what was the shot of the day - a delicate bunker shot from a tricky lie on seven to within a few centimetres of the hole.
The two-time Charles Tour champion made a 6m putt on the par four 8th to continue his momentum and then made a solid par on the 9th to set up his chance at history.
"It would be hard to beat nine holes like that in pro golf. The guys are telling me it hasn't been done before."
Brown's nine hole score beat the effort of the best nine holes recorded on the PGA Tour - Corey Pavin had an eight-under 26 on the front nine of the first round of the 2006 US Bank Championship in Milwaukee.
His playing partners Luke Toomey and Daniel Pearce were lost for words.
"It was pretty damn impressive," said Pearce. "Luke and I enjoyed watching that a lot. It was something that I have never seen before. It was some of the best golf that I have ever witnessed. That 10 hole stretch was flawless. His control was the most impressive thing. He never really looked flustered."
Leaderboard
127 Mark Brown
130 Vikrant Chandra
132 Ryan Chisnall, Richard Lee
134 Josh Geary, Daniel Pearce, Harry Bateman
