Chasing 122 for victory, Bangladesh depended on an unbroken 56-run sixth-wicket partnership between Afif, who hit 37, and Nurul, who made 22, to achieve their target with eight balls to spare in Dhaka.

Shakib Al Hasan made 26 but Bangladesh were in trouble at 67-5 in the 12th over when Mahedi Hasan departed, stumped off Adam Zampa for 23.

Pace bowler Mustafizur Rahman took three wickets to restrict Australia to 121-7 despite 45 by Mitchell Marsh, who got the same score in his side's opening loss of the five-match series on Tuesday.

"It's very pleasing to see Afif and 'Sohan' stand up, carry us to the end. Showed maturity," skipper Mahmudullah Riyad said after the win.

"And up front our bowlers did very well to restrict them to 120. But Shakib was very important with bowling and batting, shows how important he is to the team."

Bangladesh, who recorded their first ever T20 win over Australia in the previous match, have won two successive games against their opponents for the first time across formats.

Pace bowlers Josh Hazlewood and Mitchell Starc struck early to remove openers Soumya Sarkar, for nought, and Mohammad Naim, for nine, respectively.

Shakib made the hosts fight back with his 17-ball knock and a partnership of 37 for the third wicket with Mahedi.

Medium-pace bowler Andrew Tye bowled Shakib and Mahmudullah dragged the ball from left-arm spinner Ashton Agar onto his stumps as Bangladesh slipped.

But the 21-year-old Afif showed composure to thwart the opposition bowling along with Hasan, a wicketkeeper-batsman, and take the team home.

Earlier the tourists, who lost the opener after being bowled out for 108 in their chase of 131, collapsed from 99-3 to 106-7 after Marsh's wicket.

Marsh put on 57 for the third wicket with Moises Henriques, who scored 30, after the departure of the two openers.

Marsh was caught behind off fast bowler Shoriful Islam before Mustafizur struck twice on successive deliveries to send skipper Matthew Wade back for four and Agar for nought.

"Should have got high 130s or 140s, which would have been a winning score on that track," said Wade.

"The bowlers from both teams have done really well. Bowling isn't the problem for us, got to tidy up with the bat."

The third T20 is on Friday with all the matches to be played at the same venue.