Australia have overcome their first real challenge at the Netball World Cup, producing a big second half to beat Malawi 70-46 in Cape Town and clinch a semi-final place.

The Diamonds lost a quarter for the first time in the tournament with Malawi outscoring Australia 15-12 in the second stanza to force a 28-28 tie at half-time.

For the first time in five games in the tournament, Australia looked a little rattled as they were on the wrong end of a 9-2 run in the second quarter.

Coach Stacey Marinkovich made a couple of changes at half-time and the Diamonds reasserted themselves, outscoring world No.6 Malawi 21-9 in each of the last two quarters to remain top of their pool.

Australia upped the pressure and forced more turnovers and did a better job of feeding the ball to their shooters, who made a combined 92 per cent of their attempts.

The winning margin was the closest of any of Australia's games with Malawi keeping the Diamonds to their lowest score in the tournament and recording the largest total against the world No.1.

Vice-captain and goal attack Steph Wood had her most influential game of the tournament, making 18 of 19 attempts and adding 13 assists in a player-of-the-match performance.

"I felt like my shooting percentage hadn't been great, so today I knew that I needed to make sure that I shot a higher percentage, so I ticked that box," Wood told Fox Sports.

Sophie Garbin (28/32) continued her prolific form when she came on after half-time for Cara Koenen (14/15), while Keira Austin (10/10) completed a strong collective shooting effort.

Australia scored four in a row near the end of the first to lead 16-13 at the end of the quarter in which the Diamonds tallied the only three gains.

Malawi scored the first two goals of the first quarter to get within one, but a 6-1 run in Australia's favour swelled their advantage to six before the African nation then enjoyed their purple patch.

After half-time, Marinkovich brought on Garbin and Jo Weston, who came on at goal defence for Sarah Klau.

Garbin scored the first three goals of the second half and a more assertive Australia never relinquished their advantage.

"It was like building the pressure, we needed to defend for four seconds and we were able to get a fair bit of ball in that third quarter and to convert off it, which was really important for us to push that lead out," Wood said.

"Malawi were incredible today, they are a nation that's really hard to play against.

"It's getting to that end of the competition where the games will get closer and it's perfect for us leading into our game against England."

The teams have a break on Wednesday with Australia facing their biggest challenge on Thursday against England.

The world No.3-ranked side beat Fiji 89-28 later on Tuesday to secure their place in the semi-finals.

In the other group two from New Zealand, South Africa and Jamaica will make the last four.