The Kings, who are making their debut this season and had been beaten 55-20 by the Canterbury Crusaders and 46-30 by the Wellington Hurricanes in the past two weeks, had been expected to be well beaten by the table-topping Brumbies.
"Our mindset wasn't right from the start and while we got some points on, we turned off and let them back in," Brumbies captain Ben Mowen said. "Inconsistency has cost us but certainly ... you have got to give credit to them."
The Brumbies had started the game like it was a contested training session, taking control of the ball, recycling and building phases to march down field and set up Christian Lealiifano's penalty and tries to Henry Speight and Joe Tomane.
While Lealiifano missed both conversions, the ruthless efficiency the home team displayed to quickly establish a 13-0 lead suggested it would be an easy stroll to a bonus-point victory.
The Kings, however, whose line speed in defence and ability to hold the ball through phases has made them combative, went to their strength and got back into the game.
Loosehead prop Schalk Ferreira finished off an impressive move that involved constructive running interplay from the forwards.
While Brumbies scrumhalf Nic White kicked a long-range penalty to give the home side a nine-point lead, the Kings simply regrouped and responded and flanker Wimpie van der Walt crashed over from a rolling maul following an attacking lineout.
Lealiifano added a late penalty to give his side some breathing room at 19-14 heading into halftime, but the Kings struck back shortly after the re-start when they swept down field and du Preez sauntered over.
Lealiifano edged the home side 22-21 ahead again with his third penalty and when Ferreira was yellow carded for persistent infringement with 13 minutes remaining and the Brumbies flyhalf slotted two more penalties the game looked over.
The Kings, however, achieved a succession of penalties after the fulltime hooter, hammered away at the Brumbies line and were rewarded when du Preez barged over and replacement Demetri Catrakilis added the game-tying conversion.
"All credit to the boys we fought back in that final 10 minutes," Kings captain Andries Strauss said. "We are growing as a side and hopefully in the future we can win these types of games.
"We don't really want to get ahead of ourselves. We are happy with this, we would have liked to have got a win but will put this behind us and prepare for next week's game against the (Melbourne) Rebels."