TWICKENHAM (AFP) - Adam Ashley-Cooper scored a hat-trick of tries as Australia ended Argentina's hopes of a first World Cup final appearance with a 29-15 win at Twickenham on Sunday.
The Wallabies will now face defending champions New Zealand, 20-18 winners over South Africa on Saturday, in next weekend's final.
Australia and New Zealand, the only two unbeaten teams at this tournament, will be bidding to win the World Cup for a record third time.
Australia led 19-9 at half-time after Rob Simmons' early try was followed by two from Ashley-Cooper.
The valiant Pumas, who came from 14-0 down to beat Australia 21-17 last year for their first win in the southern hemisphere Rugby Championship, narrowed the gap.
But Ashley-Cooper's third try, 10 minutes from time, sealed a win for Australia, the reigning Rugby Championship title holders who have undergone a revival since coach Michael Cheika took charge last year.
Fly-half Nicolas Sanchez kicked all of the Pumas' points with five penalties, in front of an 80,025 crowd that included Argentina football great Diego Maradona.
Defeat meant Argentina, also beaten semi-finalists in 2007, will now face South Africa in Friday's third-place play-off.
Argentina recalled centre Marcelo Bosch, back from suspension, in their only change to the side that overwhelmed Ireland 43-20 in the quarter-finals.
Australia made three changes with the fit-again full-back Israel Folau and No 8 David Pocock returning in place of Kurtley Beale and Ben McCalman respectively.
Pocock, badly missed at the breakdown by Australia in their nailbiting 35-34 quarter-final win over Scotland forced several turnovers on Sunday.
A dry day made conditions ideal for running rugby and it took Australia just 68 seconds to score the game's first try when lock forward Simmons intercepted Sanchez's inside pass.
Bernard Foley added the easy conversion and Australia led 7-0.
Fly-half Foley was then involved at the other end when, after Argentina exploited a huge gap in Australia's cover, he made a try-saving tackle on Bosch.
But an offence in the build-up led to an easy penalty for Sanchez.
Thoughts of an immediate Argentina revival were dashed when Australia scored their second try in the ninth minute.
A knocked-on tap and go from Pumas scrum-half Martin Landajo led to an Australia scrum, much improved under he guidance of former Argentina hooker Mario Ledesma, before Foley's miss-pass freed left wing Ashley-Cooper for a try in the corner.
Foley kicked a tricky conversion and Argentina, who scored two early tries against Ireland, now found themselves on the receiving end with Australia in charge at 14-3.
The Pumas suffered another setback when in-form wing Juan Imhoff went off injured in the 18th minute.
Argentina forced a 23rd-minute scrum penalty and Sanchez, becoming the tournament's leading points scorer as he passed the 79-point tally of Scotland's Greig Laidlaw and South Africa's Handre Pollard, cut Australia's lead to 14-6.
Argentina, however, found themselves a man down in the 26th minute when lock Tomas Lavanini was sent to the sin-bin by English referee Wayne Barnes for a 'no-arms' tackle on Folau. The sheer speed as much as anything else prevented a fair challenge.
Things got worse for Argentina when influential skipper and hooker Agustin Creevy went off on the half hour mark.
Australia were now encamped in Argentina's 22 and the pressure told when another miss-pass, this time from centre Matt Giteau, sent in Ashley-Cooper for his second try.
Foley did not convert, but Australia were 19-6 up before Sanchez's third penalty cut their lead to 10 points.
That was how the match stayed until the break but it could have been so different had the Pumas scored a try in the closing moments of the half.
Argentina wing Santiago Cordero broke clear and offloaded to Juan Martin Hernadez but, in sight of the line, the centre's pass went behind full-back Joaquin Tuculet and the chance was lost.
In the second half, Sanchez kicked two penalties either side of a Foley effort to leave Australia 22-15 in front.
Argentina pressed hard in the final quarter before a cross-field run by Drew Mitchell opened up their defence and led to a try for fellow wing Ashley-Cooper.