Olympic champion Mollie O'Callaghan says she has just come through one of the toughest periods of her swimming career, but still overcame a packed field to win 100m freestyle gold on night one of the Australian Open Swimming Championships. O'Callaghan won the blue-riband event in 53.12 ahead of fellow Olympian Meg Harris (54.03) and Alexandra Perkins (54.21). But after a disrupted return to the pool following a hard-earned rest to recover from her stunning Paris Olympics, O'Callaghan can be positive about how she backed up. "It feels weird to be back racing," O'Callaghan told ABC Sport on pool deck at the Sleeman Sports Centre on Brisbane's south side. "For myself, I'm at a different stage compared to everyone else, I've had a different type of break and a different lead-in to this comp. "I've just been focusing on myself." O'Callaghan, who is a two-time Olympian at just 21 years old, went into the Paris Games under extraordinary pressure after a series of stunning performances as a teenager, including three individual world titles in the 100m (2022 and 2023) and 200m freestyle (2023). She is the first to acknowledge she puts a lot of the pressure on herself, but it's hard to argue she didn't perform. Five medals, three of them gold, including the much-anticipated 200m freestyle against teammate Ariarne Titmus — who is not competing in Brisbane this week — put O'Callaghan in rarefied air as one of the top performers of last year's Games. The effort of that took its toll though, leading to a well-earned break. "I had about five months off post-Olympics," O'Calaghan said. "I had the rest of 2024 off where I was, like, gonna live life. "Forget about swimming, flying around, travelling. I was enjoying it, just being able to do stuff for once. "Personally for myself, I didn't feel like I had a social outlet or a life outside of swimming, especially being 20 years old." After any lengthy lay-off, returning to full action can be tough, and O'Callaghan admitted she struggled. "It's been a long process, it's a bit of a chain reaction, like your body is under panic because I'm trying to play catch up to everyone else," she said. "I haven't really had a full week where I feel like I've done the proper training or have done the full set of training without modifications because my body's just been on constant shut down. "I felt like I've been knocked back quite a few times heading into this comp, so I've been having a lot of support from my team around me to try and set my mental space up because I know that I don't think I'm going to be on par with what I did last year and I've just got to accept that this is going to take time. "At the end of the day, LA [2028 Olympics] is four years away and you've got to make sure you're in the right headspace for them." O'Callaghan has a busy program of events this week despite her lack of training, but by letting go a little of the enormously high expectations she has of herself, she was able to relax and win gold. "I kind of told myself there's no pressure to perform here because of my circumstances," she said. "It's myself that puts pressure on me and I've looked back and reflected and I'm like, 'oh, I gotta give myself a little bit of a break'. "I'm still tough on myself, I still, through the sessions, get a bit frustrated, a bit angry, because I'm not physically capable of doing things like I'm used to. "I have been working with my psychologist and we've been thinking about different processes and perspectives on racing and I felt like today I could think about executing the race properly rather than the outcome. "Leading up to this I've been really nervous and doubting myself in a way, being like 'I'm not gonna be where I wanna be', because I'm always hungry for more and I wanna be the best, and that's the part of sport. "But I was also quite excited to see what I'm capable of doing after such a long, difficult period. Despite the challenges, O'Callaghan has still come away with another piece of gold to add to her burgeoning collection. Featuring two of the Paris Olympic finalists and three of the gold medal-winning 4x100m relay team, the 100m field was stacked. Shayna Jack (54.56) was only fast enough for fifth behind 18-year-old Bond swimmer Hannah Casey (54.52). "It's a stacked field and it's a privilege to race against a stacked field," O'Callaghan said. "At the end of the day, those girls are the ones pushing me to be better and I'm pushing them to be better and that's what makes us such a dominant and strong country. "We take from each other and we learn and we grow as athletes and I think that's the important part. "We all lean on each other; I know I can turn to any of these girls and run and tell them whatever I want and they're always there for me. "We don't view each other as competitors, more as a family in a way. So it's kind of nice to know that outside of a competition, we're together. "In the water, it's a competition and we're gonna fight over it, but we can leave it behind at the end of the day." McEvoy claims 50m fly In the other events, Cam McEvoy won 50m butterfly gold with an impressive 23.18, having swum within 0.02 of his personal best (23.09) in qualifying that morning. He did not set the fastest time of the day though, with Italian guest swimmer Thomas Ceccon setting an all-comers record of 23.00 in the heats before withdrawing from the final. "I gave it a crack, I almost got it back, I was, what, 0.09 behind him?" McEvoy told ABC Sport. "But he's 2023 world champ in this event and like ninth best ever in history in terms of top 10 rankings. "So he's a good guy to compare myself to with this event, especially with LA coming up." Ceccon, who has been training with St Peter's Western for the last couple of months, won the 200m backstroke in 1:55.71 to meet the qualifying standard for the World Championships. Olympic silver medallist Elijah Winnington claimed gold in the 400m free, but was unimpressed with his time of 3:45.97, just ahead of St Peter's Western teammate Ben Goedemans (3:47.03). A challenging return to the pool has meant he is not exactly where he wants to be, telling ABC Sport he needed to go "back to the drawing board". "I've gotta keep working," he told ABC Sport. "Internationally there are guys going 3:39 so, as much as a 3:45 in season isn't too bad, there's guys going six second faster that I'm trying to chase down." Harrison Vig (S9) won the multi-class men's 400m freestyle with an impressive 4:25.53, while Hannah Price (S10) claimed the women's title. In the men's 100m breaststroke, Paris Olympian Sam Williamson tore down the opening 50 metres and hold on to claim the title in a time of 1:00.46. He edged out a fast-finishing Bailey Lello (1:00:66) and Olympic semi-finalist Josh Yong (1:01.15) for the podium spots. In the 200m individual medley, Olympic finalist Ella Ramsay cruised home in 2:10.05 to claim gold ahead of Tara Kinder (2:11.29) and Isabella Boyd (2:13.13). Multiple Olympic champion and Paris bronze medallist in the 200m medley Kaylee McKeown cooly swam a 2:08.58 in qualifying on Monday morning — the second-fastest time in the world this year — but opted not to swim the final. Paris Olympian Lani Pallister claimed gold in the 800m freestyle ahead of New Zealand's Erika Fairweather and open water specialist Moesha Johnson. Jack Ireland (S14) won the 200m freestyle multi-class event, with Dylan Logan (S15) winning the 50m multi-class race.