The Brumbies have edged the Western Force 39-38 in a thrilling try fest at HBF Park in Perth.
The Force were trailing 20-3 in Friday night's Super Rugby Pacific match when Banks was sent off in the 29th minute for what had appeared an accidental head clash with Toni Pulu.
Pulu had just gathered the bouncing ball five metres out from the try line when Banks put his arms up to attempt a tackle.
The Force flyer slightly changed his running line in the split second before the clash of heads.
Pulu fumbled the ball as he attempted to touch it down for a try, but on review the referee decided Banks had committed a red card offence with the head clash.
The Force were awarded a penalty try, and then ran in another three tries to one during the 20 minutes the Brumbies were down to 14 men.
But Andy Muirhead's hat-trick ensured the Brumbies snatched back the lead, with the visitors holding their nerve at the death to extend their perfect start to the season to 6-0.
The Force had a late chance to steal the points, but they lost the ball from a line-out.
Brumbies coach Dan McKellar didn't think it should have been a red card to Banks.
"It's a high-speed, high-collision game," McKellar told Stan Sports.
"Banksy is coming across at full speed, TP changes direction and there's a head clash.
"If Tom Banks has a nasty bone in his body or goes out there to deliberately hurt someone, then I don't know the bloke.
"I thought the decision was wrong, and as a game we have to look at those sort of things."
The Force were made to pay dearly for a host of costly errors early in the match.
Brumbies winger Muirhead's turn of speed set up a try to Lonergan after just 83 seconds.
Muirhead scored himself in the ninth minute following a fumbled kick-off reception from Force forward Brynard Stander and 12 phases of pressure.
It was 20-3 after 17 minutes when Brumbies centre Len Ikitau set off under his own posts, shook off two tacklers during his 50-metre sprint, before offloading Banks, who sprinted the remaining 50 metres to touch down.
Banks' red card in the 29th minute saw a big momentum shift.
Although Muirhead was able to score his second try in the 34th minute - following another dropped kick-off reception from the Force - the home side ran in 28 points themselves.
Jake Strachan's try was particularly impressive, with the Force fullback smothering Lonergan before collecting the ball and shaking off a tackler in his stumbling run to the line.
The Force's lead was short-lived after Muirhead scored his third, but a second try to Force flyer Manasa Mataele in the 61st minute - when he picked off a pass and ran 70 metres to the line - ensured for a thrilling finish.
Brumbies 39 (Tries: R. Lonergan, Muirhead 3, Banks, Frost, Cons: R. Lonergan 3/6, Pens: R. Lonergan 1/1) FORCE 38 (Tries: Penalty try, Godwin, Strachan, Mataele 2, Cons: Prior 3/3, Strachan 1/1, Pens: Prior 1/1)
FORCE: 15 Jake Strachan, 14 Toni Pulu, 13 Kyle Godwin, 12 Bayley Kuenzle, 11 Manasa Mataele, 10 Jake McIntyre, 9 Ian Prior, 8 Brynard Stander, 7 Kane Koteka, 6 Fergus Lee-Warner, 5 Izack Rodda, 4 Jeremy Thrush, 3 Santiago Medrano, 2 Feleti Kaitu'u (c), 1 Harrison Lloyd
Replacements: 16 Andrew Ready, 17 Bo Abra, 18 Greg Holmes, 19 Tim Anstee, 20 Ollie Callan, 21 Issak Fines-Leleiwasa, 22 Reesjan Pasitoa, 23 Byron Ralston
BRUMBIES: 15 Tom Banks, 14 Tom Wright, 13 Len Ikitau, 12 Irae Simone, 11 Andy Muirhead, 10 Rod Iona, 9 Ryan Lonergan (c), 8 Pete Samu, 7 Jahrome Brown, 6 Rob Valetini, 5 Nick Frost, 4 Darcy Swain, 3 Sefo Kautai, 2 Lachlan Lonergan, 1 Scott Sio
Replacements: 16 Billy Pollard, 17 Fred Kaihea, 18 Tom Ross, 19 Tom Hooper, 20 Rory Scott, 21 Lachie Albert, 22 Hudson Creighton, 23 Jesse Mogg
Referee: Angus Gardner
Assistant Referee: Graham Cooper, Jordan Kaminski