The hosts posted a middling 154-6 after opting to bat in Melbourne, but the Sri Lankan batsmen finally found their feet to reach 155-5 with one ball remaining, ending the series 4-1 in Australia's favour.

Mendis batted positively, but sensibly, with captain Dasun Shanaka (35) in an 83-run partnership which powered Sri Lanka to their first win against Australia in any format since 2017.

Seamer Kane Richardson took 2-28, but Australia's second-string bowling attack never looked threatening after conceding 54-2 in the powerplay.

"When we come to the World Cup (in October), we will be really prepared," Shanaka said. "We could have done better in this series."

Reduced to 13-2 after five overs, Australia struggled to build any partnerships of substance as Dushmantha Chameera (2-30) and Lahiru Kumara (2-34) troubled the batsmen with pace.

Aaron Finch's summer, in which the skipper scored 78 runs at a strike rate of 92, ended with a whimper when he was caught on eight.

Matthew Wade struck 43 not out in the back end of the innings to drag his side to a competitive score.

"It (154) probably just wasn't quite enough at the end," Finch said.

"Sri Lanka are a very dangerous side and to win four games in a row was really good."

Australia now prepare for their first test on Pakistani soil since 1998, scheduled to begin on March 4, while Sri Lanka's next assignment is a T20 series in India starting on Thursday.