New Zealand, seeking its first title after being runner-up twice, swamped South Africa by seven wickets in Bengaluru to end the league engagements with four straight wins.
The Group B semi-final line-up will be decided on Sunday when 2009 champion England takes on Pakistan in Chennai and the West Indies clashes with India in Mohali.
England leads the group with six points, the West Indies and Pakistan have four each and India have two, setting the scene for two absorbing contests.
In New Delhi, Australia restricted Ireland to 91 for seven after electing to field and then breezed past the modest target with 40 deliveries to spare in a one-sided contest.
Ireland made a promising start by reaching 53 for one before six wickets tumbled for 38 runs.
Kim Garth (27), Cecelia Joyce (23) and Clare Shillington (22) did well at the top of the order but the rest of the batting faltered as Megan Schutt finished with three for 29.
Elyse Villani hit 43 and Ellyse Perry remained unbeaten on 29 as the Southern Stars handed itself an emphatic win by the 14th over.
Australian captain Meg Lanning credited the bowlers for the victory
“Our bowlers set the tone early,” she said. “Ireland got away in the PowerPlay, but then to restrict it to 91 allowed our batters to play freely.
“We have built a good momentum in this tournament and are ready to go.”
“There were flashes of good play but our inexperience showed in the end. It was a good tournament but no one wants to lose four in a row. We'll try to make sure it does not happen again.”
In Bengaluru, South Africa was shot out for 99 after being sent in to bat by New Zealand, with Sophie Devine and Leigh Kasperek grabbing three wickets each.
The White Ferns replied with an opening stand of 57 between skipper Suzie Bates, who hit 29 off 25 balls, and Rachel Priest, who smashed a run-a-ball 28.
Both openers fell in the space of two overs, but Devine hit an unbeaten 27 with three fours and a six to complete a dominant all-round performance.
Bates said she was confident from the start of the tournament that her team could make the semi-finals.
“We were very confident coming into the tournament,” she said. “We had a very good series against Australia which we won 2-1. The balance of the side was good, so I knew we would go far if we played good cricket.”
Bates said the team’s approach will not change heading into the semi-finals.
South Africa’s captain Mignon du Preez said her team may have failed to qualify for the semi-finals, but insisted she was determined to sign off on a happy note.
“We did not execute our plans against a good side like New Zealand and this was very disappointing,” she said. “But we want to win against Sri Lanka on Monday because it is important to end the tournament on a high.”
Australia beat Ireland by seven wickets in New Delhi
Ireland 91-7, 20 overs (Kim Garth 27, Cecelia Joyce 23, Clare Shillington 22; Megan Schutt 3-29)
Australia 92-3, 13.2 overs (Elyse Villani 43, Ellyse Perry 29 not out; Kim Garth 2-24)
New Zealand beat South Africa by seven wickets in Bengaluru
South Africa 99 all out, 19.3 overs (Marizzane Kapp 22; Sophie Devine 3-16, Leigh Kasperek 3-19)
New Zealand 100-3, 14.3 overs (Suzie Bates 29, Rachel Priest 28, Sophie Devine 27 not out)
India v West Indies (1530) Mohali
England v Pakistan (1930) Chennai
Team Played Won Lost NNR Points
New Zealand 4 4 0 +2.4 8
Australia 4 3 1 +0.6 6
South Africa 3 1 2 +0.4 2
Sri Lanka 3 1 2 -0.5 2
Ireland 4 0 4 -2.8 0
Team Played Won Lost NNR Points
England 3 3 0 +0.7 6
West Indies 3 2 1 +0.8 4
Pakistan 3 2 1 +0.3 4
India 3 1 2 +1.1 2
Bangladesh 4 0 4 -2.3 0