Umar Akmal's [ Images ] sparkling 64 from 31 balls lifted the Pakistanis to a competitive total of 167 for eight and excellent bowling from Mohammad Aamer [ Images ] and Umar Gul strangled Australia, who slumped to 144 all out in the 19th over.
Pakistan struggled with the bat after winning the toss and stumbled to 47 for four.
However, Akmal settled immediately and struck three huge sixes and seven fours to change the momentum of the match.
Pakistan looked on course for a large total but the return of Shaun Tait [ Images ] to the Australian attack held them back.
The fast bowler bowled Abdul Razzaq [ Images ] (7) with the first ball of his spell and deceived Akmal with a superb slower delivery as Pakistan struggled in the closing overs.
David Warner and David Hussey [ Images ] added 52 for third wicket but both fell in quick succession and Cameron White [ Images ] and Michael Hussey [ Images ], whose extraordinary innings lifted the Australians to an unlikely win in the World Twenty20 semi-final in St Lucia, also failed to build on solid starts.
Aamer completed figures of three for 27, Gul two for 13 and Ajmal three for 26 as Pakistan clinically dismantled the Australian tail.The second and final match of the Twenty20 series takes place on Tuesday before the teams meet in two tests in England [ Images ].