Mitchell Marsh hit an attacking half-century to help Australia recover from losing two early wickets in their chase of 210 to defeat Sri Lanka in a key World Cup clash on Monday.

Five-time winners Australia bundled out Sri Lanka for 209 in 43.3 overs at Lucknow's Ekana Stadium in the match that will give one of the teams a first win.

Australia lost veteran batsmen David Warner, for 11, and Steve Smith, for a duck -- both out lbw to left-arm quick Dilshan Madushanka in the same over.

The left-handed Warner reviewed his decision but the tracker showed the ball would have kissed leg stump and the batsman returned back fuming.

Marsh stood firm and reached his fifty -- a first in the World Cup -- in 39 balls laced with nine boundaries with Marnus Labuschagne for company. Australia reached 75-2 in 12 overs.

Earlier leg-spinner Adam Zampa returned figures of 4-47 as Sri Lanka collapsed after a 125-run opening stand between Pathum Nissanka (61) and Kusal Perera (78).