Digby Ioane, Lachie Turner and James Horwill all scored twice, while Rob Horne and Radike Samo also touched down and James O’Connor kicked 20 points on his first start at fly-half.
The Barbarians’ defence was embarrassing and they conceded 42 second-half points, but they did give the 51,212 crowd a late cheer with a consolation try for England rugby league international Sam Tomkins.
Danny Cipriani kicked two first-half penalties for the Barbarians.
South African lock Victor Matfield captained the invitational team in the last game after a stellar 110-cap career.
At the other end of the scale, Tomkins was playing his first rugby union game, a week after facing Australia in the Four Nations final, and did not look out of place.
The Wigan full-back started on the wing and could have scored in the first half had Bryan Habana not ruined a scintillating break with a careless forward pass.
O’Connor twice kicked the Wallabies into the lead, first with a penalty and then a drop-goal, and he will compete with Cipriani to start at fly-half for the Melbourne Rebels next season.
Australia’s first try came after Stirling Mortlock ran out of the defensive line, leaving a gaping hole in the Barbarians defence for Ioane to score.
The Wallabies were reduced to 14 men when prop James Slipper shoulder-charged Cipriani late, but the Barbarians could not take advantage and Australia secured an 18-3 half-time lead with a try in the corner from Turner.
It was one-way traffic after the interval as Australia found their accuracy with four tries in 13 minutes.
First replacement James Horwill charged over, then Horne struck after Salvatore Perugini was sin-binned.
Horwill added his second before Turner took advantage of another scything break from Ashley-Cooper. Ioane drove through two defenders to bring up the half-century and Samo’s burst from the scrum completed the rout.
The Barbarians scored with the last play of the match when Cipriani picked up a pass off the deck and Tomkins scored in the corner.
Scorers: Barbarians: Try: Tomkins. Pens: Cipriani 2. Australia: Tries: Ioane 2, Turner 2, Horwill 2, Horne, Samo. Cons: O’Connor 7. Pen: O’Connor. Drop goal: O’Connor.
Barbarians: Toeava, Tomkins, Fruean, Mortlock, Habana, Cipriani, Stringer, Thomson, Bergamasco, Kaino, Matfield (c), Shaw, Marconnet, Mealamu, Guinazu. Subs: Strauss, Perugini, White, Bortolami, Kenatale, Kahui, Rabeni.
Australia: Ashley-Cooper, Turner, Horne, Barnes, Ioane, O’Connor, Genia, Dennis, Pocock (c), Higginbotham, Sharpe, Simmons, Ma’afu, Nau, Slipper. Subs: Moore, Alexander, Horwill, Samo, Hodgson, Phipps, Tapuai.
Referee: R Poite (Fra). Attendance: 51,212.