Lauren Jackson broke the all-time Olympic scoring record as Australia overcame China 75-60 to reach the last four.
Jackson, playing in her fourth Games, finished with 12 points, and her final lay-up in the fourth quarter was enough to edge her ahead of Janeth Arcain with 536 points in Games competition.
The Opals had surrendered a first-quarter lead to be trailing at half-time and throughout most of the third quarter.
They finally got back in front with a little under two minutes remaining in the third with a 6-0 run that made it 55-50 on a lay-up from Liz Cambage, who led all scorers with 17 points.
Australia then outscored China 20-8 in the final period to make the final score look a little easier than it was.
'We've been really up and down and having to catch people,' said Jackson afterwards. 'This was one of those games that's a real slug-out and we didn't really get ahead until the fourth quarter - but it's good (to win).'
Jackson was less keen to talk about her own record, though, adding: 'It's nice, but this is a team sport and I can't be happy with something (that's just me).'
Australia will next face the USA, who ran out 91-48 winners against Canada and remain on track for a record fifth straight Olympic gold medal.
They recorded their 39th straight Olympic win in emphatic style against their North American neighbours.
'Canada is a team that wants to play at their pace,' said USA guard Sue Bird. 'I thought for the first time in this Olympics we got out to a really aggressive start, we put our style of play on to them and made them play at our pace.
'That's a big thing about Canada. I've played them numerous times, they're a tough team that really make you work, but I think we made them work today.'
Russia held off Turkey 66-63 in a dramatic finish to seal a semi-final place as Birsel Vardarli came up empty with a three-point attempt on the buzzer.
The European champions, who have won bronze in the last two Olympics, had held a 12-point lead early in the second half but found themselves locked in a tense fourth quarter after Turkey came back to tie it.
Isil Alben fouled Evgeniya Belyakova, who followed a theme in splitting her throws to make it 66-63 with 10 seconds left.
Turkey worked an opening for Vardarli, but her three-point shot bounced back off the rim as time ran out.
Russia will face France, who defeated the Czech Republic 71-68, in the semis.
France stormed back from a 13-point deficit late on to stun their opponents, Celine Dumerc leading the way with 23 points and six assists, while Endine Miyem added 14 points.