In short:

Australia's women will face the USA in the Water Polo World Cup semifinal, a repeat of the 2000 Olympic gold medal match at the same venue.

Australia's men's team stunned defending world championship gold medallists Spain in a stunning shoot-out to progress to the semifinal too.

What's next?

Australia's women play the USA at 6:30pm AEST on Friday, while the men will play Hungary on Saturday, also at 6:30pm AEST.

It's been 26 years since Australia and the USA paved new ground for women's water polo, contesting the gold medal match at the Sydney Olympics.

Now, in the same pool used in those Games, the Stingers and the USA will meet once more, this time in a semifinal of the World Cup Finals.

"The moment's not lost on us," Australian skipper Bronte Halligan told ABC Sport.

"I hadn't made that connection yet, that the Aussie girls played the US in the final [at the Sydney 2000 Olympics], but now you've mentioned it, that is another thing.

"But no, it's not lost on us.

"Any game's an important game and a semi's a semi; you win, or you lose, and we're going to go in there and battle our little butts off and see what we can do, and then hopefully produce a really good result."

The Sydney Olympics water polo tournament was a groundbreaking one for the sport in so many ways.

For a start, it was the first to ever feature a women's competition, despite women competing at World Championships since 1986 and in World Cup competitions since 1979.

Australia's women were pivotal in getting water polo included, with player Liz Weekes threatening legal action if women weren't included and some 50 players protesting at Sydney Airport in 1997 when the president of World Aquatics, then known as FINA, arrived in the city.

Those players were vindicated and their dream realised, women finally permitted to play Olympic water polo — the oldest team sport at the Games.

Australia and the USA made it to the final of the six-team competition, playing out a thrilling final in front of 17,000 supporters at the Sydney Olympic Park Aquatic Centre.

And it was the Stingers who came out on top, winning 4-3 after a last-second goal to Yvette Higgins.

A four-year-old Halligan attended those Games, although the now 29-year-old was not among the thousands who were there for that historic final.

But now she and her Stingers teammates have an opportunity to repeat history.

And not just history from a quarter of a century ago either — these two teams met in the semifinal of the Olympics in Paris too, the Aussies winning 14-13 after a heart-stopping penalty shootout.

That victory saw the Stingers progress to the final, where they fell agonisingly short of a gold medal against Spain.

The USA and Australia have continued to cross paths though — it was against the USA that the Stingers had a pre-tournament training camp last week in Brisbane.

"We know them as a team. We know them as a squad," Halligan said.

"They're a bunch of phenomenal athletes; they're really tough opponents.

"We're lucky to have trained against them last week; we can kind of foresee what we're coming up against, but it's not going to be an easy game, and we've got to just stay united."

To Halligan, who spent most of the 5am training sessions from the age of 14 at the Sydney Olympic Park Aquatic Centre, this pool feels like home, which made the fact that she marked her 200th international appearance with a dramatic 15-14 win over Italy.

"It kind of all just fell into place," Halligan said.

"It became this really special moment here in Sydney, in a pool that I grew up training in and with my family and friends at a huge event in a World Cup quarterfinal.

"It just was kind of almost picture perfect.

"I just feel lucky that it all kind of fell into place and this is what happened."

Halligan noted how special it was to see some of her former teammates and trailblazers in the stands — and that is exactly what the USA felt too.

The USA powered into the semifinal with a dominant 14-8 against China on Wednesday after meeting with some of their silver medallists from those 2000 Games.

"We heard from some of the players last night, and that was so amazing. Just taking us back, and learning our history," said 20-year-old USA driver Emily Ausmus, who scored four goals in that game.

"It was so cool to see the women before you that paved the path, and that got women's water polo into the Olympics.

"It's so cool that we're in the same venue; it's still so beautiful."

Beautiful and set to be packed for another massive Australian-USA clash.

"It's so important to have all the friends and family here, and especially the Stingers alumni," Halligan said.

"They've paved the way for us and a bunch of them have played with us; I saw a bunch of my ex-teammates here in the stands, and they're so special because they all have touched our careers.

"We just feel fortunate to be able to play a big game like this and play it here in Sydney."

Sharks 'showed we belong', stun champions Spain

On Thursday night, the Aussie Sharks also channelled the class of 2000, stunning reigning world champions Spain in a thrilling penalty shoot-out.

Australia were four goals down at one stage of the match, trailed 6-3 at quarter time, 16-13 at three-quarter time and 18-16 with 40 seconds to play.

However, the side fought back incredibly to level the scores late on at 18-18.

And, on a night of extraordinary drama at the Sydney Olympic pool, the Sharks had to equalise twice inside the final 10 seconds.

Marcus Berehulak, bandaged after being opened up by a stray Spanish fist in the first half, thought he had scored the leveller with six seconds to play, only for it to be taken off him by the referees for taking a free throw inside the six metres zone.

As the parochial Sydney crowd booed the decision, the Aussies kept their heads as they were told to replay the final 7.9 seconds.

With the Sharks keeper up to create an extra man, Matthew Burns powered home the actual leveller at the near post with 1.1 seconds to play to set up penalties.

Substitute keeper Laurence Barker saved from Fran Valera in the shoot-out, while Australia slotted all five of their penalty shots to claim a 23-21 victory.

The victory was fitting for an Australian team that have embraced the underdog tag but, just as they did in Paris against Serbia, stunned the favourites with a never-say-die display of pure grit.

"Congratulations to Spain," player of the match Jacob Mercep, who led the Sharks with six goals, said.

"They had us in the first half, but we were able to come back.

"We were kind of manifesting this semifinal; we've been talking about it all winter.

"When it matters the most, we showed we belong."

Berehulak scored four, Matthew Byrnes — who slotted the final penalty — scored three, while veteran Blake Edwards added two.

"I got stitched up, and I'm glad I came back out there because that win was incredible … nothing like I've felt before," Berehulak said.

"Spain is a fantastic team, but I think we really stayed composed. We had a game plan that we stuck to, and we just kept chipping away.

"Having that crowd, and being able to deliver a performance against the current world champions — it tops my number one water polo memory of all time."

Captain Nathan Power, Charlie Negus and Nicolas Constantin Bicari all scored one each.