SINGAPORE -- There was nothing separating Australia's five-time Olympic champion Mollie O'Callaghan and American Claire Weinstein at the halfway mark of the women's 200m world championship freestyle final. Stroke for stroke. Length for length. A four-lap race for global supremacy.
And then came the second 100m.
As we so often see in these major meet races, when O'Callaghan hits the turbo button, nobody on the planet is capable of going with her. She swam the third 50m almost a second quicker than Weinstein, then completely motored away from the field over the final lap to stack yet another gold medal on her already remarkable resume.
Just like compatriot Kaylee McKeown 24 hours earlier, O'Callaghan wasn't the fastest qualifier for her final, but she expertly rose to the occasion in the gold medal race with a time of 1:53.48, the quickest anyone has gone in the event this season. In many ways, it was a repeat of her effort in Paris last summer, when she swam over the top of Dolphins teammate Ariarne Titmus to capture her first individual Olympic title. Except this time there was no Titmus, who is taking a break from the sport.
But don't let that discredit O'Callaghan's latest achievement; the Australian still had to overcome a stacked field, including 18-year-old Weinstein, who owned the second-fastest event time this year, New Zealand's Erika Fairweather, and China's Bingjie Li, who passed Weinstein late to take the silver medal.
"Heading into this week has been a whirlwind," said O'Callaghan, moments after jumping out of the pool. "Having a big long break after the Olympics was well needed and then coming back from injury myself. I am so thankful to have an amazing coach [Dean Boxall] to guide me through this difficult time.
"I know it has been hard for a lot of people to come back after the Olympics, but I am very grateful to have good support from the team to get me through this mentally and physically."
O'Callaghan etched her name further into swimming's record books on Wednesday evening in Singapore, becoming the first person in the sport's history to twice win world championship crowns in both the 100m and 200m freestyle events. Mastering both races -- the sprint and the patient sprint -- has long been viewed as one of the greatest challenges in swimming. For O'Callaghan, she is making it appear routine.
The 200m victory was O'Callaghan's 10th gold medal at the world championships, to go along with five Olympic gold medals. The 21-year-old appears to be on an inevitable path to becoming Australia's most decorated swimmer.
Also on night four of pool action in Singapore, Australian rookie Harrison Turner won his country's first medal at a world championships in the men's 200m butterfly, finishing third behind American Luca Urlando and Poland's Krzysztof Chmielewski. Turner's time of 1:54.17 set a new Australian record in the event.
"I looked up on the board and I had to look there for a bit, I was like: 'Does it say third?'," said an elated Turner. "It's just unreal."
French superstar Leon Marchand shattered Ryan Lochte's world record in the 200m individual medley. The four-time Olympic champion from Paris 12 months ago lowered the mark by a mind-boggling 1.31s with his time of 1:52.69 in the semifinals, collecting a US$30,000 bonus in the process. Marchand is only contesting the individual medleys this week.
Australian sprint star Kyle Chalmers qualified fourth-fastest for Thursday night's men's 100m freestyle final. The surprise of the semifinals was China's world record holder and Olympic champion Pan Zhanle missing out on a place in the gold medal race, having posted only the 10th-best time in preliminaries.
It was also hard luck for Australian distance specialist Sam Short, who was forced to withdraw from the men's 800m final after coming down with a bout of food poisoning since taking silver in the 400m race on night one.
With competition in the pool now at the halfway point, Australia sits atop the medal tally with four golds, a silver, and three bronze medals.
Here's how night four in Singapore unfolded: