Amir returned career-best figures of 5/30 to bowl Australia out for 307 in 49 overs after Pakistan chose to field first. David Warner (107) starred with a hundred while skipper Aaron Finch scored 82.

Mitchell Starc (2/43) then broke the crucial 64-run eighth wicket partnership between captain Sarfaraz Ahmed (40; 48b, 1x4) and Wahab Riaz (45; 39b, 2x4, 3x6) before removing Amir for a duck in the same over as the defending champions sealed the issue in 45.4 overs with the run out of Sarfaraz.

The result saw Australia bounce back to winning ways after losing to India in their last game, while Pakistan failed to get a win since upsetting England after their tie against Sri Lanka was washed out.

Chasing 308 for victory, Pakistan lost Fakhar Zaman early but Babar Azam (30) and Imam Ul-Haq (53) shared a 54-run stand before the former was dismissed by Nathan Coulter-Nile.

Mohammed Hafeez (46) and Imam then joined hands for a 80-run stand but once both were out in quick succession, the chase lost steam before Sarfaraz and Wahab revived their hopes again.

But Wahab edged one to wicketkeeper Alex Carey off Starc, which was initially ruled not out only for the reviews to show otherwise. From there on, there was no coming back for the 1992 champions.

Pat Cummins (3/33) was the pick of the bowlers for Australia.

Earlier, Warner scored his first hundred since the Sandpaper Gate fiasco before Amir stole the show. His figures are the best by a Pakistan seamer in a World Cup since Wasim Akram's 5/28 against Namibia in 2003.

Warner -- whose last two fifties off 74 and 77 deliveries, respectively, were the slowest of his one-day international career -- had a point to prove and the dashing southpaw took 111 balls to get to his 107, studded with 11 fours and one six.

Skipper Aaron Finch supported him well with a belligerent 82 off 84 balls (6x4, 4x6) as the pair added 146 runs for the opening wicket. But Amir dented Australia's run-flow with crucial wickets while young Shaheen Shah Afridi (2/70) also did well with the ball.

Pakistan made amends for their initial failure as the bowlers failed to make the most of the overcast conditions and the seam movement that was available off the pitch after skipper Sarfaraz Ahmed put the Aussies in.

Pakistan were poor in the field, dropping a few catches, including one each of Finch on 25 and Warner on 104. On both occasions, Asif Ali was the culprit and the bowler was Wahab Riaz.

The defending champions were off to a dream start with Warner and Finch going great guns. Finch brought up his 22nd ODI fifty in 63 balls by hitting Mohammed Hafeez for consecutive boundaries and then smashed a six as he was particularly severe on the 38-year old off-spinner.

Amir broke the partnership and it was Finch who paid the price for his needless urgency, holing out to Hafeez at mid-wicket in the 23rd over. Former skipper Steve Smith failed on the day, his leading edge caught by Asif at mid-wicket off Hafeez.

From there on, the Aussies could not get partnerships going as Pakistan reined in, largely due to Amir's incisive spell. Warner was lucky to get to his hundred when a thick outside edge raced to the third-man fence, as the southpaw celebrated in his trademark style.

He finally walked back to the hut for 107 after being caught by Imam-ul-Haq off Shaheen Afridi. Since Warner's dismissal, Australia managed just 64 runs for the loss of six wickets, losing five wickets for just 21 runs between overs 45 and 49.

Brief Scores: Australia: 307 all out in 49 overs (David Warner 107, Aaron Finch 82; Mohammed Amir 5/30); Pakistan: 266 all out in 45.4 overs (Imam ul-Haq 53, Mohammed Hafeez 46, Wahab Riaz 45, Sarfaraz Ahmed 40; Pat Cummins 3/33, Mitchell Starc 2/43, Kane Richardson 2/62)