Johnson, a sophomore, scored both goals, and senior Megan Anstotz played a strong all-around game as fifth-seeded Audubon (17-6) continued a powerful tournament run with its second consecutive Central Jersey Group 1 title.
The Green Wave, which upset fourth-seeded Holy Cross and top-seeded New Egypt en route to Monday's sectional final, advanced to face the South Jersey champion in Thursday's state semifinals at Eastern.
"I'm speechless," Johnson said. "I can't stop smiling."
Morgan Driver scored the only goal for sixth-seeded Haddon Heights (13-7), which also knocked off two higher-seeded teams on its way to the title game.
"It was one of those games that could have gone either way," Haddon Heights coach Melissa DelCollo said. "There were two plays in the first half and another one in the second half where the ball was bobbling around in front of their goal, but it just would not go in the cage for us."
Johnson gave Audubon a 1-0 lead with 5:39 remaining in the first half. On a corner, Johnson took an insert from Sarah Urban, dodged a defender, and blasted a shot into the cage.
Haddon Heights nearly tied the score late in the first half, but Audubon goalie Miranda Mistalski, who finished with nine saves, made a couple of clutch stops on a scramble in front of the cage.
"Haddon Heights is a great team," Audubon coach Thea Ricci said. "They came to play today."
Haddon Heights tied the score at 1 with 19:12 remaining in the second half when Driver chased down a long pass that had hopped over an Audubon defender's stick and eluded another defender before Driver lifted it into the cage.
The teams appeared headed for 7-on-7, sudden-death overtime when Johnson took possession on a restart just outside the circle.
"I just stepped inside [the circle] and shot it," Johnson said. "I'm not even sure what happened."
Less than 90 seconds later, the Green Wave were celebrating their second straight sectional title.
"This is what these girls have worked for every single, solitary day since August," Ricci said. "It's the ultimate."
Haddon Heights 0 1 – 1
Audubon 1 1 – 2
Goals: HH-Morgan Driver; A-Julie Johnson, 2.
Saves: HH-Maresa Malcolm, 5; A-Miranda Mistalski, 9.
Contact staff writer Phil Anastasia at 856-779-3223, panastasia@phillynews.com, or @PhilAnastasia on Twitter. Read his blog, "Jersey Side Sports," at www.philly.com/jerseysidesports