Australian captain Aaron Finch insists he is happy with his team's depth a few months out from their T20 World Cup defence, despite an amazing innings from Sri Lanka captain Dasun Shanaka denying them a sweep of their three-match series.

A fine all-round performance from Marcus Stoinis (38 off 23 balls and 2-8 off two overs) had Australia well placed for victory, but the home team produced a sensational finish to secure a dramatic four-wicket win.

Chasing 177 at the Pallekele Stadium in Kandy on Saturday, Sri Lanka, who failed to reach 130 in the first two games, slumped to 6-108 In the 16th over.

But an unbroken seventh-wicket stand of 69 between Shanaka (54 off 25 balls) and Chamika Karunaratne (14 off 10) then swept them to an improbable win as they thrashed 59 off the last three overs.

The Australian quicks lost their discipline as Shanaka blasted five fours and four sixes, with Josh Hazlewood conceding 22 runs in the 18th over after giving away just three off his first three.

Jhye Richardson (1-46 off four) leaked 18 off the 19th over, leaving the home team needing 19 off the last.

Kane Richardson (0-44 off 2.5 overs) started the 20th with two wides as he looked to bowl yorkers outside off stump.

Shanaka sent the sell-out crowd into a frenzy later in the over by blasting 14 off three deliveries, before Richardson sent down another wide to gift Sri Lanka the winning run.

Australia went into the game without three of their specialist bowlers in pacemen Pat Cummins and Mitchell Starc and spinner Adam Zampa plus a fourth member of last year's World Cup winning side, all-rounder Mitch Marsh, who missed the game with a minor calf strain.

Finch, named player of the series after scoring 114 runs at an average of 57, was happy with the depth of the team a few months out from their home defence of the World Cup.

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"We've seen over the last 12 months that we haven't had a full quota of players to pick from at certain times so we've had to mix and match and we've had some really good results as well, so we're really comfortable with the depth of the team," he said.

Australia made 5-176 after Finch won the toss for the third time in as many matches.

Finch (29 off 20) and David Warner (39 off 33) got Australia off to a swift start with an opening stand of 43 off 5.4 overs.

Stoinis helped his side recover from losing wickets off three straight balls in mid-innings after they were well placed at 1-85 after 9.5 overs.

Steve Smith (37 not out off 27) made his highest score in his last nine T20I games.

Stoinis was called upon to bowl his first overs of the series and he dismissed Pathum Nissanka (27 off 25) and Charith Asalanka (26 off 19) after the home team reached 1-67 in the ninth over.

But even after taking three more wickets and looking certain winners, Australia couldn't close out the game.

The five-match ODI series between the two teams starts at the same venue on Tuesday.

AAP