The five-time champ was stuck in fourth place in the opening heat of the six-star event with just three minutes remaining.
But the Australian showed her mettle at the death as she found a late wave before unleashing a series of well-connected turns to bag the day's highest scoring ride of 8.77.
It was enough to send her through as heat winner.
“It was tough out there to find waves, the girls had me up against the ropes right ’till the end but fortunately I found a good wave and got the score” said Gilmore.
“I find it difficult surfing in heats with four in the water and without priority. My opponents in that heat were extremely hungry for waves, it’s not easy especially in smaller conditions like today but I’m through and it’s good.”
Gilmore's compatriot Sally Fitzgibbons, seeded second in Newcastle, had an altogether less stressful path through her heat with two eight-point-plus rides.
“That was a fun heat for me, when you find the right wave there’s some fun sections that connect to allow for excellent scores” said Fitzgibbons.
Hawaii's Bethany Hamilton struggled in the inconsistent, peaky conditions and was sent tumbling out of the competition by Pauline Ado of France and Australia's Felicity Palmateer.
Larger swells and adverse weather are expected towards the end of the week on the New South Wales coastline, forcing organisers into a slight rescheduling of the event. Men's world champion Joel Parkinson is now to surf his opening round encounter early on Wednesday, with Gilmore also penned in for the morning session.
Hunter Ports Women’s Classic of 48:
Heat 1: Tatiana Weston-Webb (Haw) 15.16, Cannelle Bulard (REU) 11.67, Sarah Baum (ZAF) 10.36, Paige Hareb (NZ) 6.9
Heat 2: Nage Melamed (Haw) 15.00, Sage Erickson (USA) 12.83, Dominic Barona (Ecu) 10.96, Nao Omura (Jpn) 8.37
Heat 3: Alize Arnaud (Fra) 16.67, Sofia Mulanovich (PER) 12, Eden Putland (AUS) 9.13, Sarah Phelan (AUS) 2.1
Heat 4: Stephanie Gilmore (Aus) 14.60, Dimity Stoyle (Aus) 13.07, Naomi Stevic (Aus) 12.24, Kirby Wright (Aus) 11.97
Heat 5: Joanne Defay (Fra) 13, Lakey Peterson (USA) 11.26, Laura Macaulay (Aus) 8.33, Quincy Davis (USA) 7.4
Heat 6: Pauline Ado (Fra) 13.33, Felicity Palmateer (Aus) 11.66, Freya Prumm (Aus) 9.73, Bethany Hamilton (Haw) 5.5
Heat 7: Ellie-Jean Coffey (Aus) 13.83, Keely Andrew (Aus) 12.60, Justine Dupont (Fra) 12.07, Rebecca Woods (Aus) 11.30
Heat 8: Alessa Quizon (Haw) 15, Courtney Conlogue (USA) 13.93, Codie Klein (13.06), Leila Hurst (Haw) 11.47
Heat 9: Sally Fitzgibbons (Aus) 16.50, Bronte Macaulay (Aus) 14.87, Anali Gomez (Per) 11.93, Maud Le Car (Fra) 11.63
Heat 10: Stephanie Single (Aus) 13.07, Philippa Anderson (Aus) 13.00, Alana Blanchard (Haw) 10.57, Brodie Doyle (Aus) 8.57
Heat 11: Bianca Buitendag (Zaf), Nikki Van Dijk (Aus) 15.26,Mikaela Greene (Aus) 12.74, Rosanne Hodge (ZAF) 12.03
Heat 12: Laura Enever (Aus) 13.17, Brittani Nicholl (Aus) 12.64, Georgia Fish (Aus) 6.5, Joanne Dennison (GBR) 4.70
Burton Toyota Pro Round of 144 results:
Heat 19: Taylor Clark (USA) 11.67, Kiron Jabour (Haw) 9.5, Saxon Lumsden (Aus) 9.47, Asher Wales (7.97)
Heat 20: Cory Arrambide (USA) 16.5, Dillon Perillo (13.9), Jake Sylvester (Aus) 11.36, Brent Dorrington (Aus) 8.87
Heat 21: Chris Friend (AUS) 14.27, Michael February (Zaf) 12.80, Ian Gentil (Haw) 10.87, Dane Bird (Aus) 9.33
Heat 22: Heath Joske (Aus) 16.77, Dylan Goodale (Haw) 14.20, Chris Salisbury (Aus) 14, Kaito Ohashi (Jpn) 8.93
Heat 23: Manuel Selman (Chl) 12.27, Nick Squires (Aus), Dean Bowen (Aus) 5.7, Tanner Hendrickson 4.87
Heat 24: Mitchell James (Aus) 12.96, Darren O’Rafferty (Aus) 12.77, Arashi Kato (Jpn) 11.33, Chase Wilson (USA) 8.77