The Lions preserved their 100 per cent tour record with a 22-12 victory over Queensland Reds
They were given a punishing workout just two weeks before returning to Suncorp Stadium and a first Test appointment with Australia.
After scoring 128 points and 17 tries in battering the Barbarians and walloping Western Force, the Lions had to dig deep following a breathtaking early try from Reds wing Luke Morahan.
Scrum-half Ben Youngs claimed a close-range touchdown for the tourists, while fly-half Owen Farrell kicked 17 points, but there was another possible fitness concern when centre Manu Tuilagi departed nursing a shoulder injury midway through the opening period.
Props Cian Healy (ankle ligaments) and Gethin Jenkins (calf muscle) were already booked on flights home tomorrow.
Their replacements Alex Corbisiero and Ryan Grant have flown in from Argentina and South Africa, respectively.
The Reds conjured touchdowns for Morahan and scrum-half Nick Frisby - Quade Cooper kicked one conversion - yet the Lions ultimately prevailed following a game of high intensity and ferocious commitment watched by a 50,000 crowd.
The Reds flew out of their starting blocks, putting the Lions under immediate pressure as half-backs Cooper and Frisby toyed with a stretched defence before home wing Rod Davies was tackled just short.
For the first time on tour, the Lions found themselves thoroughly tested in all areas, but they released almost 10 minutes of unremitting pressure when Tuilagi freed wing Tommy Bowe from deep.
Ireland star Bowe ran brilliantly before finding his fellow wing Alex Cuthbert, yet the Welshman was denied a try by Morahan's superb tackle that completed another breathless passage of play.
The Reds were hell-bent on moving possession wide and at pace, yet the Lions showed signs of scrum and lineout dominance that underpinned Farrell's opening penalty strike after 14 minutes.
Morahan, though, then scored one of the greatest individual tries of any Lions tour when he produced a stunning 70-metre break that initially took him through Cuthbert's tackle and around Ben Youngs.
Lions skipper Sam Warburton was also brushed aside before Morahan had the presence of mind to kick final defender Stuart Hogg, gather the rebound and touch down.
Cooper converted, and then Tuilagi departed after just 20 minutes to be replaced by Wales wing George North, who went into midfield alongside his countryman Jonathan Davies.
A second Farrell penalty narrowed the gap to a point, but Cooper missed a penalty chance 35 metres out that he should have landed as the game's astonishing pace showed no sign of relenting.
North's speed caused problems for the Reds' defence, and his approach work carved open the Australian side, but Farrell lost possession as he attempted to ground the ball under pressure from Morahan, and a golden chance went begging.
The Lions, though, only had to wait another three minutes before claiming their opening try, resulting from Youngs robbing Reds number eight Jake Schatz of possession at a scrum five metres out and sniping over.
Farrell added the extras, and only some last-ditch tackling from the Reds prevented a Warburton score after North ran strongly from deep, before Farrell slotted his third penalty as a pulsating first half drew to a close.
Farrell kicked a fourth penalty 10 minutes into the second period, and with rain making conditions difficult for both sides the Lions adopted a more pragmatic approach through the back-row forwards' direct running.
Reds flanker Beau Robinson was carried off after being caught flush in the face by a charging Vunipola, which caused a lengthy stoppage while he was carefully treated by medics before being helped away with his neck in a brace.
Frisby scored a second try for the Reds 16 minutes from time, but Cooper missed a simple conversion attempt, meaning the Lions held a seven-point advantage as Paul O'Connell appeared off the bench.
And with props Adam Jones and Dan Cole also on, the Lions were able to close out a win that was sealed by Farrell's fifth penalty three minutes from time.