The Bulls overcame an early scare to overwhelm their neighbours the Lions 48-27 and take the last Super Rugby playoff place after Saturday's derby at Loftus Versfeld.
The home side outscored the Lions by seven tries to two, despite going behind after 16 seconds, and will now go away to face the Hurricanes in next weekend's quarterfinal.
The Bulls were 31-19 ahead at half-time in a convincing performance as the regular season came to a close, leaving eight teams left to chase for the title in the playoffs.
For the Lions, it ended a run of three successive trips to the final where they finished runners-up on each occasion.
Hanro Liebenberg, Marco van Staden, Lizo Gqoboka, Burger Odendaal, Cornal Hendricks, Handre Pollard and Manie Libbokscored the tries for the home side with Pollard converting five of them and adding a penalty.
Hacjivah Dayimani and Cyle Brink got the Lions tries with one conversion from Elton Jantjies, who also kicked over four penalties. Fullback Andries Coetzee also contributed a dropkick.
The Lions went ahead straight from Pollard's kick-off as Aphiwe Dyantyi fielded the ball, setting off on a mazy run through the home defence before offloading for eighth man Dayimani to power his way over and dot down.
But the Bulls responded almost immediately as Liebenberg finished off a pick-up-and-drive and Van Staden, Gqoboka and Odendaal were also over the opponents try line before the break.
The Lions took every kicking opportunity they could to keep down the deficit. They would have grabbed a playoff place had they picked up a bonus point.
When Bulls lock RG Snyman was sin-binned, Brink's try brought the score back to 31-27 but the Bulls then turned on the power, dominating in all areas to score three more tries and secure a well-earned victory.