The Young Lions never gave up, even after the hosts took a 41-38 lead with four minutes left on the clock, and their last attack ended in the winning try in the corner for replacement back Thulani Shabalala.
It was the visitors from Johannesburg who finished the strongest of the two Gauteng sides by eventually scoring six tries, five conversions and a penalty goal, while the men from Pretoria responded with five converted tries and two penalty goals.
The Vodacom Bulls will wonder what went wrong, as they led 24-3 in the first half, only to see their southern neighbours claw their way back in the game to lead by 31-24 after 15 minutes in the second half.
The hosts then scored twice again to make it 38-31, but the team from Johannesburg were not done and drew level again at 38-all with seven minutes to go.
A penalty goal by JT Kapank (flyhalf) close to the end seemed to seal the deal for the Bulls, but the Lions were not done and after opting for an attacking lineout from a late penalty, they did what was needed with Shabalala crossing in the corner for the winning try right at the death.
Lions flyhalf Matt Coetzee, who is in matric at Jeppe Boys' High School in Johannesburg, was named the Player of the Match after scoring two tries and succeeding with all but his final kick at goal.
In the end, it was heartbreak for the hosts who managed to defeat the Lions by a single point, 32-31, in their league encounter two weeks ago at the same Pretoria venue, which enabled them to finish the league standings unbeaten after winning all five regular games.
However, the thrilling final was a testament of the Lions’ determination and never-give-up attitude and they showed remarkable character to keep their composure at late in the match after Kapank's second penalty goal from long range gave the hosts a three-point lead.
From the restart, the Lions then went up-field in search of the winning score, and after they had managed to win a penalty that was within kicking range, they elected to kick to the corner to set up a possible maul try.
The Lions surprised the home side to quickly recycle the successful lineout, moving the ball with pace and accuracy down to the flank where replacement Shabalala was on hand to take the final pass and perform a spectacular dive for a dramatic winning try in the corner.
Coetzee failed with the sideline conversion, but that was the end of the match, which left the young Bulls and their fans heart-broken and jubilation for the winning side.
Scorers:
Vodacom Bulls 41 (24) - Tries: Marco Ferreira (2), Demitre Erasmus, Stephan Brits, Juandre Schoeman. Conversions: JT Kapank (5). Penalty goals: Kapank (2).
Fidelity ADT Lions 43 (10) - Tries: Ricardo Brandao, Morne Venter, Matt Coetzee (2), Zian Cilliers, Thulani Shabalala. Conversions: Coetzee (5). Penalty goal: Coetzee.