Australia 105 for 7 (Christian 39, Rahman 2-9, Mahedi 2-17) beat Bangladesh 104 for 9 (Swepson 3-12, Tye 3-18) by three wickets
Dhaka: Australia have recorded their first victory on their tour of Bangladesh in another gritty, bowler-dominated encounter after cameos from allrounders Dan Christian and Ashton Agar broke the back of a tricky run-chase.
Mustafizur Rahman (2-9 off four overs) was once again near unplayable, reducing his series economy rate to less than four as the visitors teetered on the brink of a fourth consecutive defeat on another tough Dhaka pitch.
But Christian, who pummelled 39 off 15 balls including five sixes off one over after a surprise elevation to first drop, and Ashton Agar (27 off as many deliveries) ensured the Aussies came home by three wickets.
Australia had restricted the hosts to 9-104, their lowest score of an extremely low-scoring series, as recalled leg-spinner Mitchell Swepson led another strong bowling performance.
Agar departed to a stunning late catch from Shamim Hossain but his 34-run stand with Ashton Turner (nine not out) was vital after their side had lost 5-18, with Andrew Tye (four not out) then scampering a single to seal victory with an over to spare.
Australia's decision to tweak their tactics and send Christian in at No.3 proved inspired as the 38-year-old blasted fellow allrounder Shakib Al Hasan for five sixes in an over, all between long-on and mid-wicket.
Christian is the first Australian to hit five sixes of an over in a T20I, while the 30 runs he scored was the equal most scored off by an Aussie in a single T20I over, matching Aaron Finch and Glenn Maxwell (who took 30 off Bilawal Bhatti at this very venue at the 2014 T20 World Cup) and Ricky Ponting (who smashed four sixes off Daryl Tuffey in the first ever international T20 in 2005).
Despite scoring nearly a third of the required runs in five blows, the remainder of the chase was far from a cakewalk.
Mustafizur delivered a knockout opening salvo, having Christian caught at point and delivering a wicket maiden, surely one of the few ever delivered in the final over of the Powerplay.
The ensuing procession off wickets once highlighted Australia's inability to come to terms with what are extremely challenging batting conditions.
Ben McDermott and Alex Carey were both trapped lbw, the latter by a big-spinning delivery from Mustafizur.
Moises Henriques was unfortunate to be run-out at the non-striker's end off a deflection, while Mitch Marsh (11) was bowled by off-spinner Mahedi Hasan on his outside edge for his lowest score of the series.
Captain Matthew Wade had been bowled in the opening over.
Australia rejigged their bowling line-up for the fourth match, resting hat-trick hero Nathan Ellis having played his first match of the tour the previous evening, and Adam Zampa, but their replacements – Swepson and Andrew Tye – gave strong accounts of themselves.
The fine form of series leading wicket taker Josh Hazlewood (2-24 off four overs) continued, snaring the key scalp of Shakib, who would have been out for a duck if an lbw appeal off Ashton Agar was reviewed.
He failed to make the Aussies pay however, with his 15 off 26 balls the slowest innings of his 83-game international T20 career.
Opener Mohammad Naim (28 off 36), Afif Hossain (20 off 17) and Mahedi Hasan (23 off 16) all made handy contributions, but the loss of regular wickets hamstrung their ability to build up any momentum.
Swepson (3-12 off four overs) proved the most difficult to get away, ripping fast leg-breaks into the spin-friendly surface while also proving a handful with his wrong'un as he trapped captain Mahmudulluah and Nural Hasan both lbw without scoring.
Tye's 3-18 off three overs capped a solid return to the side with wickets off the last two balls of the innings.