Australia 25-13 Fijipublished at 69 mins
But Australia, perhaps with fresher legs on from the bench, draw a penalty and Bernard Foley will have a shot at goal.
It looked as though skipper Akapusi Qera was the man to blame on that occasion.
Pool A result: Australia 28-13 Fiji
Australian win first match but no bonus point
David Pocock two tries in four minutes
Prop Sekope Kepu scores second-half try
Match played at Cardiff's Millennium Stadium
Brendon Mitchell
But Australia, perhaps with fresher legs on from the bench, draw a penalty and Bernard Foley will have a shot at goal.
It looked as though skipper Akapusi Qera was the man to blame on that occasion.
Fiji are dragging themselves back into this game and in the second half it is Australia's discipline which has faltered, with the Wallabies (white dots) conceding four penalties in dangerous positions. Fiji have only been punished twice, and that was in the Australian half.
A Fijian knock-on sees Nick Pipps called into action for the first time though, inserting at a scrum just inside opposition territory.
And James Slipper, though back to his feet and able to walk, will certainly play no further part. Scott Sio's back on in his place.
Nick Phipps is also on at scrum-half, replacing Will Gnia.
#bbcsport
Dave Fassam: Australia are looking good, but Fiji look a little tired. Got to question the fixture lists in RWCs!
Ewan Clark: Fiji have been sloppy today.
John M Butt: Too many rules now at the breakdown. Too many penalties and yellow cards. It’s time the rules were thinned down to let the game flow.
The Wallabies line-out has fast become a bit of a mess here, as another Stephen Moore throw is grabbed by a white-shirted player.
But as the counter-attack breaks down, there's a bit of concern for Australia's James Slipper and Fiji's Peceli Yato, who clashed heads in the tackle. A sore one.
Rob Jones
Former Wales scrum-half on BBC Radio 5 live
"They've given themselves a chance with that try. It's been all Fiji over the last 10 minutes They got that forward drive, Volavola throws the dummy and then it's all about momentum."
Not if the Wallabies have anything to do with it, and they'll have a penalty after a high tackle from replacement Nemia Soqeta on wing Rob Horne.
Bernard Foley thumps the ball out of play - Fijian defence now needs to be as sharp as their recent attacking.
And it is! They steal the line-out and clear.
Australia 25-13 Fiji
Superb, just superb. Fly-half Ben Volavola, who once represented Australia's Under-20 side at the World Junior Championships, dances past the first tackle and then rolls past the next to touch down under the posts.
Nemani Nadolo converts, Fiji are 12 points behind.
They couldn't, could they?
This is developing into a brilliant watch as Fiji continue to play with speed and enterprise.
A warning to Australia captain Stephen Moore too, as replacement Greg Holmes is penalised for coming in at the side.
To touch we go. At this point, the non-Australians in the crowd are backing only one team...
The Flying Fijians are playing right on the edge here, trying everything with ball in hand. This is a now-or-never moment in time.
All the while, Australia make a double change in their front row as Scott Sio and Sekope Kepu are withdrawn for James Slipper and Greg Holmes.
Fiji are enjoying their best period of the second half, but still it's Australia who have overwhelmingly dominated possession and territory in the last 10 minutes.
Stephen Moore has the line-out and Australia secure the ball, but Waisea Nayacalevu is steady under scrum-half Will Genia's big up and under.
Fiji have the ball but they're in the wrong part of the field.
Right intent, wrong execution. Gabiriele Lovobalavu is the guilty party, sending a floaty pass over the head of Nemani Nadolo and out of play.
Their accuracy has to improve if they're to remain in with a shout.
Rob Jones
Former Wales scrum-half on Radio 5 live sports extra
"So far Australia have probably produced the best rugby of this tournament."
The ball is back in Australian hands soon enough though, Scott Sio, Michael Hooper and Scott Fardy all trying to punch another hole in that Fijian defence - who actually do well to draw a penalty at the breakdown.
Australia 25-6 Fiji
And wing Nemani Nadolo successfully lands the kick to reduce the arrears to 19 points.
Still lots to do for the Fijians but it is, at least, a start.
Straight from the restart, however, Bernard Foley is turned over and then penalised for coming off his feet.
Perhaps surprisingly Fiji will take the three points...
Rob Jones
Former Wales scrum-half on Radio 5 live sports extra
"That try sums up Australia, and their pace and power. Accuracy of the pass, pace when they go to deck, and everyone is comfortable with the ball in hand.
"Australia are going to be relentless now."
Australia 25-3 Fiji
And that's exactly what Australia would've wanted - and what Fiji wouldn't have wanted - to open up this second half.
The green and gold again switch the ball across in search of the fleet-footed Israel Folau, who skips past the first tackler before being brought down.
The damage is already done as the Fijians are left scrambling back though, and prop Sekope Kepu shows a lovely little step to cross from close range.
The conversion from Bernard Foley is good, and this is looking like a long 35 minutes for Fiji.
Fiji actually steal the ball momentarily, but they're immediately penalised for not releasing.
The Wallabies are wasting no time with the line-out either...