Irvine: It was the event Australia’s Lani Pallister wasn’t supposed to enter, and also the one in which Canada’s Summer McIntosh was desperate to break Ariarne Titmus’ world record.

But the opening night of competition at the Pan Pacific Championships in Irvine, California, produced a stunning upset in the women’s 200-metre freestyle as Pallister cemented her status as a serious threat at the 2028 Olympics by beating the world’s best female swimmer.

In a major shock just a fortnight after the Commonwealth Games swimming program in Glasgow, Pallister highlighted Australia’s depth in the absence of Mollie O’Callaghan by blitzing the field to touch the wall in 1:55.60, just 0.36 seconds clear of McIntosh in 1:55.96.

McIntosh, a three-time individual Olympic gold medallist, has added the 200m freestyle to her busy program and made no secret of her desire to add another world record to her glittering resume.

She said before the meet she was buzzing at the prospect of coming out on night one and trying to lower Titmus’ lifetime best of 1:52.23.

But an inability to produce her best on the opening nights of major international competitions haunted McIntosh once again – think the 400m freestyle losses to Titmus at both the 2023 world championships and 2024 Olympics – as Pallister bulldozed her way to a famous win.

Initially slated to swim the 400m, 800m and 1500m freestyle events, Pallister decided to add the 200m freestyle as a physical and mental challenge with her famous swimming mother, Janelle Pallister (nee Elford), current coach Dean Boxall and former mentor Michael Bohl, who is now involved with Chinese swimming, watching from the stands.

There was also a sense of wanting to perform on US soil two years out from an Olympics where Pallister will enter as a genuine gold-medal chance in multiple freestyle events.

“I think it’s really important to take opportunities that make you a tougher and better athlete,” Pallister said. “This is the first taste of the Olympics. Going 1:53 is wicked.”

At last year’s world championships, Pallister (second) finished ahead of McIntosh (third) in the 800m freestyle. It prompted McIntosh to declare that she never wanted to feel like that again.

But there was again shock on the youngster’s face after she had been upstaged by the Australian, whose stocks have risen significantly over the past year since she moved to Boxall’s program at St Peters Western.

Arguably more impressive was what Pallister did later in the evening, backing up to claim a silver medal in the 1500m freestyle, just 2.53 seconds shy of US legend Katie Ledecky.

Pallister’s quad and hip flexor began cramping at the 1000-metre mark as she dug deep to register a personal best of 15:38.62 and lower her Australian record. It was a statement swim and sent a clear message to Ledecky that she means business ahead of the 800m freestyle later this week – an event the American has never lost at a senior international meet.

Ledecky clearly wasn’t thrilled with her time of 15:36.09 and knows she will need to be better in two years’ time.

“I think getting up and doing a double tonight, two of the hardest doubles … I’m pretty proud,” Pallister said. “I’m stoked with it. It was survival mode.

“I’m glad that I can be a world-class swimmer, and I’m still top five all time. I get a lot more honour and pride out of racing the 1500 when you’ve got the likes of Katie there, who’s dominated this event for so long.”

The 200m and 1500m freestyle events clash on the same day at the LA Olympics in two years, meaning Pallister is likely to choose the latter.

Could she have beaten Ledecky if she had ditched the 200m freestyle, as initially planned?

“Everyone cracks that joke: ‘If my grandma had wheels, she’d be a bike’. You can’t say what would have happened,” Pallister said.

“I feel like I’ve been listening to the US anthem for almost 10 years now.”

Australia performed better than expected on night one of the four-day meet, with Sam Short (800m freestyle), Brittany Castelluzzo (200m butterfly) and Ben Armbruster (50m butterfly) also registering confidence-boosting victories for a Dolphins team coming off an outstanding Commonwealth Games campaign.

The USA came away with six victories on Wednesday evening, including a world record in the mixed 4x100m medley relay. Australia finished second.

Short’s pre-meet claim that he wanted to “smash the yanks” got off to a favourable start as he touched the wall in 7:37.02, just outside his personal best, after being under world record pace at the 500-metre mark. He is making a habit of going out hard and demoralising his opponents early in races.

The 22-year-old, who claimed three individual gold medals at the Commonwealth Games, has his eyes on breaking the 400m freestyle world record and also taking down reigning Olympic champion Bobby Finke in the 1500m freestyle, who he accounted for by 5.5 seconds in the 800m event. This was some start and Short was lapping it up.

“I was pretty fired up to try and do that,” Short said.