Superstar Eels captain Mitch Moses missed a field goal with little more than six minutes to play in a clash of NRL battlers on Sunday afternoon.
On the ensuing seven-tackle set, England-bound Sloan stepped up from beyond the 40-metre line and nailed a beautiful strike that sent the Wollongong crowd crazy.
"He annoys me at training because when we're going from drill to drill, if there's a loose ball on the ground, he just picks it up and does long-range field goals all the time," said Dragons coach Dean Young.
"It annoys me, but obviously practice pays off."
Sloan and Blake Lawrie, another long-term Dragon set for the exit door, had earlier bagged tries to keep Saints in the fight against their fancied visitors.
The win was also a fitting farewell for the home side's beloved co-captain Damien Cook, who is leaving the NRL for the Super League next season as well.
But after a disappointing year that brought the club's first wooden spoon, the Dragons will perhaps be most excited about some key moments from their next wave of stars.
Five-eighth Lyhkan King-Togia put Sloan in for a try with a deft kick down the left edge, then helped gun second-rower Dylan Egan over with a short ball on the right.
The scores were locked at 22-all when Dan Atkinson stepped inside and fended Junior Paulo before throwing a one-handed offload for Connor Muhleisen to score Saints' fourth try.
St George Illawarra also did well to fight through adversity, losing Hamish Stewart (concussion) and Val Holmes (ankle) to injury and then veteran prop Lawrie to the sin bin.
England-bound Lawrie flattened Dylan Walker as the departing Eel returned a kick-off late in the second half and sat down for his shoulder charge.
But his 10-minute spell mattered little as Saints won the game with 12 men.
The loss brings the curtain down on a season of injury carnage at the Eels, with coach Jason Ryles blasting his side's effort against the Dragons.
"Until today, I probably can't question any of the effort and the fight that we showed throughout the season," he said.
"I feel for our fans, having to sit through that.Â
"We had opportunities there but our attitude and application for periods of the game was nowhere near NRL standard and we paid the price."
Moses starred for the visitors, sending a kick up for Jordan Samrani to score the first of his two tries in the Eels' opening set with the ball.
The halfback then helped stand-in fullback Josh Addo-Carr over from a scrum before putting Walker in with a crash play.
Samrani came off late following a head clash with teammate Kitione Kautoga, while Harrison Edwards also failed to finish the game with a knee issue
