A superb forwards effort from the Brumbies handed the British and Irish Lions their first defeat on tour by 14-12 in Canberra.
The Australia side controlled the breakdown and set-pieces until 60 minutes, when the cavalry arrived off the Lions bench attemping to narrow the gap on the scoreboard.
With a severe lack of time together amongst the Lions backline and Stuart Hogg starting only his second game at fly-half, the lack of cohesion many feared before kickoff was a crippling blow to the Lions early success.
Brad Barritt, Christian Wade and Shane Williams all arrived in camp this week and combined with Hogg's inexperience in the pivot role, there were many moments in the first half where the Lions appeared understandably lost.
The sight of Williams returning in a Lions shirt at 36 was a surreal experience and nearly resulted in a dream start - the veteran Wales winger bundled into touch going for a try in the left corner.
Instead the Brumbies struck first. Confusion in the defence between Wade and Hogg gave Tevita Kuridrani too much space and he brushed off Wade to score.
Stern defence from the Brumbies and lineout woes for captain Rory Best sent the Lions backwards rather than forwards in attack, but the work of their forward pack when keeping it tight around the fringes was initially effective.
It handed Hogg a first penalty attempt, only for the ball to ricochet back off the post.
For all of the Lions problems though, the Brumbies only lead 5-0 after half an hour, squandering chances of their own and with Mogg missing a long-range shot at goal.
It took three attempts before Mogg finally found his range, converting from 40 metres out before Hogg responded to leave the Brumbies 8-3 ahead by half-time.
A furious half-time message from Andy Farrell was designed to spur the Lions into action, but early territory ended in no points with the Brumbies instead adding three more of their own by the boot of Mogg.
With the Lions missing the intensity in their one-on-one collisions that was so obvious against the Waratahs in Sydney, the Brumbies controlled the proceedings both at the set-piece and at the breakdown with worrying ease.
Some tactless physicality from Ryan Grant in the maul then handed Mogg a further three points, the Lions down 14-3 and feeling the game slip away.
Fine work by Sean O'Brien at the breakdown cancelled out the Brumbies latest penalty, before the heavyweight bench arrived.
The introduction of a new front row in Alex Corbisiero, Richard Hibbard and Dan Cole produced penalties at the scrum, only for Hogg to find the woodwork again.
With Hogg replaced by Owen Farrell, goal-kicking was never going to be an issue and the England fly-half added three points instantly to reduce the deficit to five.
It brought the Lions within range but battling against the clock and a tricky, physical Brumbies side that had reminded everybody watching why they are leaders of the Australian Conference, the task was ominous.
The work in particular of Matt Toomua at fly-half, both with his distribution and his defence, was noteworthy as the Brumbies pack toiled to keep the visitors at bay.
Farrell's second penalty, with the Brumbies not releasing, cut the lead to 14-12 with ten minutes left.
Momentum had truly swung in the Lions favour - Farrell and Conor Murray dictating as the tourists desperately searched for the three points needed to take the lead.
Hibbard called for a big scrum to create the penalty opportunity with time disappearing as the Lions opted to reset and break the Brumbies spirit. Instead it was the Lions who were crushed - the Brumbies winning the ball and clearing away.
The scenes of celebration at the final whistle spoke volumes of how much victory meant to the Brumbies and the important of these matches. Having suffered their first defeat, the Lions must now lick their wounds ahead of facing Australia in Brisbane on Saturday.
Pens: Mogg 3
For British and Irish Lions:
Pens: Hogg 2, Farrell 2
Brumbies: 15 Jesse Mogg, 14 Henry Speight, 13 Tevita Kuridrani, 12 Andrew Smith, 11 Clyde Rathbone, 10 Matt Toomua, 9 Ian Prior, 8 Peter Kimlin (c), 7 Colby Faingaa, 6 Scott Fardy, 5 Sam Carter, 4 Leon Power, 3 Scott Sio, 2 Siliva Siliva, 1 Ruan Smith.
Replacements: 16 Josh Mann-Rea, 17 Jean-Pierre Smith, 18 Chris Cocca, 19 Etienne Oosthuizen, 20 Jordan Smiler, 21 Mark Swanepoel, 22 Robbie Coleman, 23 Zack Holmes.
British and Irish Lions: 15 Rob Kearney, 14 Christian Wade, 13 Brad Barritt, 12 Billy Twelvetrees, 11 Shane Williams, 10 Stuart Hogg, 9 Ben Youngs, 8 Toby Faletau, 7 Justin Tipuric, 6 Sean O'Brien, 5 Richie Gray, 4 Ian Evans, 3 Matt Stevens, 2 Rory Best (c), 1 Ryan Grant.
Replacements: 16 Richard Hibbard, 17 Alex Corbisiero, 18 Dan Cole, 19 Geoff Parling, 20 Dan Lydiate, 21 Conor Murray, 22 Owen Farrell, 23 Simon Zebo.
Referee: Jérôme Garcès (France)
by Ben Coles