This was rugby's version of Sir Isaac Newton's third law of motion: for every action there is an equal and opposite reaction ... at least until the Brumbies conquered with a penalty try to finish the match.
Momentum swayed; neither side settled into a rhythm. The Stormers strove for a first win in their third match of four on the road trip; the Brumbies endeavoured to stay on top of the Australian conference. The lead changed four times in the first half but the ebbs and flows provided constant entertainment helped by a billiard table surface in Canberra and a lack of interference by referee Glen Jackson.
There was some bruising tackling. Defensive lines were largely unbending which made Matt Toomua's ability to ghost through four Stormers tacklers off a lineout in midfield all the more remarkable - setting up the first try for left wing Robbie Coleman.
Coleman's tenacity paid dividends in his second try too, in the game's definitive moment. He chased a Ben Mowen grubber to the left corner and seized it when Stormers wing Kobus van Wyk dithered and lost possession. Coleman prised the ball and forced his way through van Wyk.
Gio Aplon had moments of elusiveness for the Stormers and the Brumbies parted when Duane Vermeulen charged like a human cannonball after the visitors opted for a lineout 5m from the line rather than kicking a penalty.
The Stormers had the scrum advantage, bulldozing forward given the opportunity but the Brumbies had the better lineout. Ben Mowen was the star - his steals have become a habit this season. Kiwi Jack Whetton also produced a fine display in his Brumbies debut.
The Stormers never surrendered. That was demonstrated by their 70m counter-attack, again featuring Aplon, from their own line in the 71st minute when Nic White missed a penalty. Vermeulen was relentless, using his mass to surge at will.
The visitors were rewarded with a final try to Juan de Jongh in the 75th minute but the missed conversion from just to the left of the posts by Peter Grant stymied the last thrust.
Brumbies 25 (R. Coleman 2, penalty tries, N. White 2 con, 2 pen) Stormers 15 (D.Vermeulen, J. de Jongh tries, P.Grant con, pen). Halftime: 13-10.