Gumberg followed up his opening round of 65 at Kingston Heath with a 69 at the neighbouring Victoria Club on Friday to surge to nine under for the championship.
Rising star Harrison Crowe matched Gumberg's 69 at Kingston Heath, while exciting young Chinese Wenyi Ding carved out a seven-birdie 64 at Victoria to join first-round leader Herbert at eight under.
After missing the cut at last week's Australian PGA Championship in Brisbane, Ding ditched his caddie and it's so far working after the 20-year-old soared 52 spots up the leaderboard on Friday.
Crowe, the former You Tube sensation and NSW Open and amateur champion, mixed six birdies with three birdies in his rollercoaster round.
Kiwi Daniel Hillier was one stroke further behind at seven under and safely in the clubhouse after a 68 at Victoria.
Herbert and Smith both hit off just after midday, with the 2022 British Open champion making a lightning start to be three under after three holes.
Two weeks after winning the NSW Open at Murray Downs, Bendigo boy Herbert opened with a brilliant eight-under 63 at Victoria on Thursday to grab a one-stroke lead over Japanese amateur champion Rintaro Nakano and American Ryggs Johnston.
Smith shot 65 and was looking to take apart Kingston Heath on Friday after blasting officials pre-tournament for setting the famous sandbelt layout for "American-style" target golf.
Defending champion Joaquin Niemann was a major mover on Friday with a 66 at Victoria.
The Chilean LIV Golf star reeled off six birdies in a seven-hole stretch, then another two late to rise to four under for the tournament.
His playing partner Min Woo Lee is one stroke further back at three under after shaking off a dreaded double bogey on the 17th, his eighth hole of the day, in a round of 71
33°C