Late magic from Issak Fines helped the Brumbies snatch a dramatic 24-23 win over the Waratahs in Saturday's Super Rugby AU clash at ANZ Stadium.

The visitors trailed 20-5 after 33 minutes despite having grabbed an early lead through Thomas Cusack after Will Harrison failed to gather in a kick.

Two Harrison penalties moved the Waratahs ahead before Tom Horton marked his first start by spinning away from a maul to score.

Quick thinking from Harrison and James Ramm saw the latter gather the fly-half's kick to the left wing to put the Waratahs in control, but Folau Fainga'a reduced the deficit, the television match official spotting he had just grounded on the line when under pressure.

Tom Wright's run allowed Rob Valetini to score again before the break, but another Harrison penalty gave the Waratahs a six-point advantage that looked likely to be enough.

However, with only three minutes remaining, Fines found a gap to surge through beneath the posts, with Bayley Kuenzle's conversion enough to steal the victory and send the Brumbies second.