The Barcelona forward opened the scoring with a clinical near post finish on 12 minutes after fine play by Charles Aranguiz on the right-side of the area.
And he turned provider just two minutes later when his surging run ended with a pass to Jorge Valdivia who made no mistake with a stunning shot into the top corner from the edge of the box.
At this point it looked like Australia would be all set for a drubbing, but credit to the Socceroos who dug deep and reduced the arrears when Tim Cahill thumped a far post header beyond Claudio Bravo after a superb cross from the right by Ivan Franjic.
The Aussies were a different proposition in the second period and went close when Cahill had a goal correctly chalked off for offside while Mark Bresciano forced a good stop out of Bravo.
Chile were a shadow of the side that roared out of the traps but sealed victory in injury time when Jean Beausejour drilled a 20-yard shot into the corner.
PRE-MATCH: Vidal and Bresciano start. Chile's Arturo Vidal is deemed fit enough to start, despite undergoing surgery on his knee as recently as May. As for Australia, they are also boosted by the inclusion of a doubt with Mark Bresciano shrugging off a back problem to take his place in the team.
12' - GOAL! Chile 1-0 Australia. It's that man Sanchez who gets the opener. Charles Aranguiz causes chaos in the box on the right and when his dinked cross is knocked down, Sanchez is on hand to coolly fire into the near post corner.
14' - GOAL! Chile 2-0 Australia. Two in two minutes and the Socceroos have had a nightmare start. Sanchez races towards goal and picks out Valdivia on the edge of the area, who makes no mistake with a rasping shot into the top corner.
35' - GOAL! Chile 2-1 Australia. The Socceroos are back in it. Ivan Franjic hangs a ball up to the far post from the right for Cahill who leaps highest to thump a header into the corner. The ex-Everton man rolls back the years with a trademark jump. Game on!
36' Australia chance! Cahill breaks away again and takes a touch on the right of the area before fizzing in a shot that Claudio Bravo kicks away with his legs.
57' GREAT SAVE! Bravo is forced to push away Bresciano's low drive after Cahill had again caused havoc by allowing a left-wing cross to drop kindly for his teammate.
61' - OFF THE LINE! Vargas is played in by Sanchez's sensational pass and stabs a shot under the keeper, but Wilkinson gets back to hook it clear when it looked all set for 3-1.
90+2' - GOAL! Chile 3-1 Australia. Chile clinch it as Wigan's Beausejour arrows a superb 20-yard drive into the bottom corner after Pinilla's shot was well saved by the keeper.
TALKING POINT: Can Chile shock the big two in Group B? La Roja have always been regarded as dark horses in this pool, but prior to tonight everyone was expecting Spain and Holland to come through it. Chile showed in the opening 20 minutes just why they can pull off a surprise here in Brazil - but they will need to step up it up a few gears after Australia made them sweat. Sampaoli's men are comfortable playing in their home continent and after the holders' heavy defeat against the Dutch, Chile's chances have just become a whole lot stronger.
Chile have scored 3+ goals in a World Cup game for the first time since 1962.
The group containing Spain & Chile in 2010 saw just eight goals in total. This year, Group B has already seen 10 after only two games.
Alexis Sanchez has played a hand in seven of the last eight goals that Chile have scored (six goals, one assist).
Sanchez is the first Chilean to get a goal and an assist in a single World Cup game.
Tim Cahill has scored four goals in his last four appearances for the Socceroos.
That was only Chile's third win in 18 World Cup outings since they finished third at the 1962 World Cup.
(Stats courtesy of Opta)
MAN OF THE MATCH
Alexis Sanchez (Chile): La Roja flew out of the traps and it was Sanchez who shone brightest. A clinical finish and a neat assist saw him do the majority of the damage. He remained a threat in the second period when Australia pressed and could well be a star of this tournament if Chile can spring a surprise at the expense of Spain and/or Holland.
PLAYER RATINGS -
CHILE: Bravo 7, Mena 6, Isla 6, Medel 6, Jara 5, Valdivia 7, Aranguiz 7, Diaz 6, Vidal 6, Alexis Sanchez 8, Vargas 6. Subs: Gutierrez 6, Beausejour 7, Pinilla n/a.
AUSTRALIA: Ryan 6, Franjic 6, Davidson 6, Milligan 6, Spiranovic 6, Leckie 8, Oar 7, Jedinak 7, Wilkinson 7, Bresciano 7, Cahill 8. Subs: McGowan 6, Troisi 6, Halloran 6.
MATCH IN A TWEET
- Sports & Recreation
- Alexis Sanchez
- Tim Cahill
- Charles Aranguiz
- Mark Bresciano
- Claudio Bravo