Australia struggled to build partnerships having been put in to bat by Sri Lanka, their highest stand coming between Campbell Kellaway and Nivethan Radhakrishnan as they put on 46 for the fourth wicket.
Kellaway was Australia’s top scorer with 54 runs from 77 balls as the three-time champions slumped to 175 all out off the final ball of their innings.
The last three wickets fell for eight runs as Wellalage produced his second double-wicket over of the match, as he also claimed his second five-fer of the World Cup.
This time the slow left-armer went for one more run than against Scotland to return figures of five for 28, which sees him five clear in the early race to top the wicket standings.
In reply, Sri Lanka kept above the required run rate but were consistently pegged back by the Australian quicks.
Tom Whitney and William Salzmann took Sri Lanka’s second and third wickets in the space of three balls to reduce them to 41 for three in their chase of 176.
Wellalage again helped to steady the ship, this time with bat in hand, putting on a 70-run partnership with Anjala Bandara, before Bandara was dismissed sending an outside edge into the hands of wicketkeeper Tobias Snell.
Sri Lanka’s captain continued on to his half-century, coming off 69 balls and featuring four fours and one six.
With the Lions requiring just five runs, it seemed that Wellalage would steer the team home but he was dismissed caught and bowled by Whitney and it was left to Raveen De Silva to hit the winning runs as Sri Lanka emerged the only unbeaten team in Group D.
