RIO DE JANEIRO (AP) — Cate and Bronte Campbell are quite the sister act.

The Australian swimmers are both leading medal contenders heading into the Rio Olympics, though they quickly point out this isn't one of those sibling rivalries from the Serena vs. Venus Williams mold, the kind that stirs mixed emotions when they inevitably face each other for the same prize.

"It's very different (than) Venus and Serena because we're not playing against each other on the tennis court," Bronte Campbell said Tuesday. "We're swimming in a swimming pool against six other people in the race. I'm not really racing against Cate. I'm racing against myself and trying to do my best race."

Still, they are keenly aware of just how remarkable it would be to stand on a medal podium together.

"Look, it's an incredibly special thing just to be competing in an Olympic Games together," Cate said. "In 2012, after we qualified for the team together in the 50 freestyle, we both knew that we had achieved something great just by qualifying for the team."

Now, look where they are.

Twenty-two-year-old Bronte is the reigning world champion in the 100-meter freestyle, but 24-year-old Cate is the Olympic favorite after setting a world record of 52.06 seconds just last month.

The dazzling performance caught everyone off guard, no one more than Cate's little sister.

Bronte described herself as "a little bit astounded," before going on to say, "It wasn't something that we thought was going to happen. I certainly didn't expect it to happen. Our coach didn't. Cate didn't. I couldn't believe that it happened. I wasn't even at the pool when it happened. I got a phone call about it. I thought my dad was joking."

Even though Cate is riding high at the moment, she knows nothing is automatic at the Olympics.

In her first trip to the games, at the tender age of 16, Campbell captured her only individual medal — a bronze in the 50 free — and also helped the Aussies take bronze in the 4x100 free relay. But she didn't even make the final in the 100 free at Beijing.

Four years ago in London, Cate was stricken by pancreatitis and had to withdraw from the 100 free. She did manage to compete in the 50 but was eliminated in the semifinals. The highlight was being part of the gold medal-winning team in the 4x100 free relay, an event the Aussies are again favored to win in Rio — especially with Bronte now part of the mix.

"I'm almost more excited to race with Bronte in the 4x100 freestyle relay," Cate said. "That will be a really great night."

Bronte agreed.

"We've always really enjoyed racing together against the rest of the world, not necessarily against each other," she said.

The younger sister also was eliminated in the semifinals of the 50 free at London, but Bronte really began to carve out her own niche at last year's world championships in Kazan. She swept the 50 and 100 free, and joined Cate on the winning 4x100 free relay squad.

Not surprisingly given that showing, Bronte isn't conceding anything to her older sibling.

"It's all about what happens at the final, who's the fastest on that night," Bronte said. "Cate is swimming well. I see her training every day. I know what she's capable of. Breaking a world record is an amazing thing. I'm really proud of her for doing it. But it doesn't really change anything for me."

Cate insisted she is merely focused on herself, not what her little sister is doing.

"No one is going to be more upset if I don't perform than myself," the older sister said. "I can't speak for anyone else on the team, but it's a very individual and a very selfish sport. I've kind of just shrug off all the other expectations because, in the end, it's down to me. The rest of it doesn't matter."

Deep down, both sisters have surely had dreams of standing together on the Rio podium, arm in arm, each with a medal around her neck. But they have to keep it buried, to ensure they're both focused on what really matters.

They may be sisters, but they'll merely be two swimmers chasing the same thing when they take the starting block in Rio.

"It would be great," Cate said. "But for me, it's about executing a good race, and hoping that Bronte does the same thing. I can't control what anyone else does in the field, especially what Bronte does. I have to focus on what I can do."

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Follow Paul Newberry on Twitter at www.twitter.com/pnewberry1963 . His work can be found at http://bigstory.ap.org/content/paul-newberry .