Wallam was injected into the game off the bench midway through the fourth quarter to thunderous cheers from the crowd at the Newcastle Entertainment Centre and made an immediate impact.
She scored with her first touch of the ball and finished with a perfect eight goals from eight attempts, including some sensational highlight plays.
The goal shooter nailed an off-balance goal while falling out of the court before putting Australia ahead just before the final siren.
It looked like the game was heading to extra time before a brilliant Kate Moloney intercept gave the ball to Wallam, who took a giant leap from the circle edge and tossed the ball in the goal basketball lay-up style as the clock ran out.
The 28-year-old was mobbed by her teammates immediately and the roof nearly blew off the stadium as the crowd erupted.
Wallam was embraced by the entire Diamonds squad and hugged by England stars Geva Mentor and Helen Housby, who were clearly conscious of the magnitude of the occasion.
Wallam has been at the centre of the sponsorship saga engulfing Australian netball after Gina Rinehart's Hancock Prospecting tore up its $15 million deal with the sport.
Wallam, who became the first Indigenous player to represent the Diamonds in over 20 years with her debut, expressed concern about wearing the Hancock Prospecting logo on the Diamonds uniform.
She became Diamond No. 189 and just the third Indigenous netball to play for the Diamonds - after Sharon Finnan-White and Marcia Ella-Duncan.
"I was kind of relieved to get my chance on court," Wallam told Fox Netball after the game.
"It's been the toughest few weeks of my life so to finally get out there and play in this dress was really special. It kind of makes the last couple of weeks feel like a bit of a blur."
