The 2018 winner at Augusta carded 11 birdies in his sizzling 11 under par third round to go 18 under overall on the prestigious Asian Tour event.
Sub-60 rounds are extremely rare in golf.
There have been just over a dozen on the US PGA Tour and there had been none on the Asian Tour until earlier this year.
Preferred lies were played so Reed's feat does not stand officially.
Reed's scorching round at Fanling was the lowest score ever at the Hong Kong Open, Asia's oldest professional golf tournament, trumping a 60 by Ian Poulter in 2010.
"I had probably one of my worst warm-ups ever," Reed, 34, who is among a number of big-name players to have jumped ship to the Saudi-backed LIV Golf circuit, told reporters.
"I looked at my caddie and he said, 'Hey, a warm-up's a warm-up. Let's go out and just play golf. Some of your best rounds have come from a poor warm-up.'"
The American started with a blistering five birdies in a row and rattled off four more on the trot to finish with a flurry.
"I honestly felt it could have been lower," he added.
In March, Reed's then-playing partner and fellow American John Catlin carded a 59 at the International Series Macau for the first sub-60 round on the Asian Tour.
Going into the final round in Hong Kong, Reed holds a three-shot lead over India's Rashid Khan and Nitithorn Thippong of Thailand as he chases a first win on the Asian Tour.
Defending champion Ben Campbell of New Zealand is a further shot back at 14 under.
This is the 63rd edition of the Hong Kong Open.
