Enter Capitals veteran Marianna Tolo.

Requiring a 25-point or more win to secure quarter-final qualification, Tolo rolled back the clock with a vintage display under the rim, dropping 26 points and pulling in 17 rebounds to overpower a plucky Puerto Rico on Monday who looked all night to be playing the role of party pooper.

It all came in the wake of Tolo's revelation she'd spent weeks in the lead up to Tokyo unsure she would even be picked in Sandy Brondello's squad.

Now she's earned the Opals a crack against the United States, who have won the last six Olympic gold medals.

"Look, it's been such a battle to get to this point, there has been so much going on and i am just so proud of how we fought," Tolo told Channel Seven.

"You know, we didn't come out how we wanted to, and even just to fight back in that second half and really take control of the game, and win it with those two quarters is just unbelievable.

"It's a fresh start now, we're into the quarter finals and anything can happen so we're all really excited for that."

Winless in their first two matches in Tokyo after a preparation which included the shock departure of Liz Cambage, the Opals conceded the first eight points of the game against Puerto Rico despite knowing only a big win would grant them passage into the quarter finals.

They trailed by one at quarter time and led by just one at halftime, but a 51-25 second half, helped by a three-pointer and fall-away jump shot from Cayla George in the last 90 seconds, rescued the most unlikely result in a 96-69 win.

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They were then drawn to face the United States, officials pulling Australia's name from a pot in a 50-50 call that could have also seen them matched up against Spain.

Tolo was joined in prominence on the stat sheet by George, who had 19 points, and captain Jenna O'Hea who had 15 including four three pointers.

Australia led by 24 points and twice curiously turned down good looks close to the basket, before George eventually nailed the key jump shot with 28 seconds to play.

That put them ahead of the target for the first time, but there were still two missed Australian free throws to come, the Opals relying on Puerto Rico's last-ditch three point effort to miss before they could celebrate.

"I'm not sure why we came out like that," Brondello said of their slow start.

"It was like our brains froze and we forgot what we were supposed to do ... maybe it was the moment.

"I said 'this comes down to this here' (pointing to her heart) ... you've got to play with some heart. And it worked for us ... they responded in the right way and we found a way to win."

It saved the Opals - winners of three silver and two bronze medals - from their worst-ever Games result, a fifth in Rio five years ago.

But that will only be delayed unless Australia beats the United States for the first time in an Olympic campaign in Wednesday's quarter-final.

Of the United States' six consecutive Olympics wins, three have been in finals against Australia. They have a 7-0 Games record against Tolo's Opals.

But Australia beat them in their last meeting, in a Las Vegas exhibition game just hours after influential Opals centre Liz Cambage withdrew from the squad for mental health reasons.

"We've been through a lot in the last month or so and we've stayed together, stayed prepared and ready," George said. With AAP