The Victorian fan favourite has company at the top after relinquishing a four-shot halfway advantage with a grinding even-par 72 in miserable Melbourne on Saturday.
Little-known and lowly-ranked American Ryggs Johnston joined Herbert at 14 under with a birdie-filled round of 68 as 14 players ended the day within five strokes of the lead.
"I might have just let a few more people back into the tournament but I'm still leading, still where I want to be so, yeah, a good result from a frustrating day," Herbert said.
Johnston blazed through the front nine in 31 shots, catching Herbert even before the turn with his fourth consecutive birdie on the seventh hole.
A dreaded double-bogey seven on the par-5 14th was the world No.954's only blemish as Johnston continued his stunning week on the Melbourne sandbelt.
Hailing from Montana and named after Mel Gibson's iconic Lethal Weapon character, the DP World Tour Qualifying School graduate only arrived on Monday after finishing in a tie for 43rd at last week's Australian PGA Championship in Brisbane.
The 24-year-old then played this week's other host course, Victoria Golf Club, on Tuesday and had planned a practice round at Kingston Heath on Wednesday before the foul weather intervened.
Despite going into Thursday's opening round "pretty much blind", Johnston carded eight birdies - including five in a row from the 12th - and a single bogey to reach seven under par and sit one shot off the lead.
He continued the assault on Saturday to keep Herbert honest in the LIV Golf star's quest to add the Stonehaven Cup to the NSW Open crown he won three weeks ago at Murray Downs, just two hours from his hometown of Bendigo.
American Ryggs Johnston shot to a share of the lead in the third round of the Australian Open. (Con Chronis/AAP PHOTOS)
"It looks so easy for Ryggs, who doesn't probably care about the Australian Open as much as I do - with no disrespect to him," Herbert said.
"It just means so much being my home national Open. I'd love to put one of these on my resume.
"So stoked to have hung onto a spot in the final group just so you can keep an eye on everything, especially Ryggs."
Herbert and Johnston are two shots clear of a five-way pack at 12 under, including resurgent defending champion Joaquin Niemann.
After starting 10 shots back, Niemann posted a sizzling 64 to place the leaders on notice.
Newly-crowned Australian PGA champion Elvis Smylie (69), Finland's Oliver Lindell (69) and former Asia-Pacific Amateur winners Jasper Stubbs (68) and Wenyi Ding (68) of China are also only two behind.
Marc Leishman carded a 68 to be equal eighth at 11 under, three shots off the pace, along with another ex-Asia-Pacific Amateur champ Harrison Crowe (69).
The in-form Herbert, though, remains the player to beat as the 28-year-old eyes a maiden Australian Open triumph and another rare wire-to-wire victory to match his 2021 Irish Open triumph.
A defiant Cameron Smith had insisted a maiden Open crown remained in touching distance despite a dramatic second-round collapse.
Alas, the 2022 British Open champion will end his four-tournament summer stint back home winless after slumping to a tie for 49th at two under following a disappointing round of 76.
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