A Berrick Barnes three-pointer with just five minutes remaining handed the Lions' next opponents a 3-0 series whitewash despite another outstanding Welsh effort.
Wales trailed 12-9 at the break after Barnes kicked four first-half penalties to three from the impressive Leigh Halfpenny and neither side were able to pull away in the second period.
The Aussies, with bad boy Kurtley Beale back in their starting side after injury and off-the-field controversy, came close just after the interval but it was Wales who scored the game's opening try on 62 minutes.
Former Lions tourist Ryan Jones powered over from close-range after a sharp burst from Mike Phillips and a beautiful offload to Alex Cuthbert and Wales finally had some reward for the manner in which they attacked the Aussie line despite knowing the three-match series was already beyond them.
Halfpenny's simple conversion moved Wales four points clear at 16-12 and a first win on Australian soil since 1969 looked like being on the cards even though the visitors had lost skipper Sam Warburton to injury close to the half-hour mark.
But just as all three southern hemisphere giants have done against Wales, England and Ireland this summer, the Wallabies hit back when they needed to as they responded quickly and confidently.
Rob Horne did his best to drop the ball over the line under pressure from Jon Davies but fortune favoured the Green and Gold and the Wallabies were back in front just two minutes after Wales had been celebrating themselves.
Barnes' failure with the difficult extras from wide out on the right ensured the gap was just a single point as the crowd readied themselves for another nerve-wracking final 15 minutes but the Wallabies were always favourites to do what they do best and see the game out.
Halfpenny slotted his fourth penalty with 10 minutes left to play but the Wallabies showed the Lions exactly what they'll be up against next summer as they kept their composure to work their way upfield and earn another shot at goal.
Mike Harries had been the hosts' hero with Barnes off the field last weekend but it was the Waratahs playmaker who struck the fatal blow to Welsh hopes this time around. His final kick was never in doubt and once it sailed through the posts, you always fancied the Wallabies wouldn't make the same mistakes Wales made in the second rubber.
With referee Craig Joubert regularly penalising Wales at the breakdown throughout the 80 minutes - just as he had done in the first Test in Brisbane - Rob Howley's men never worked their way into a position to strike back.
Instead, the hosts stayed calm, kept it tight and, when Will Genia hammered the ball into touch, the Wallabies were home and dry…until next summer at least.