Irvine: The hopes of Australia’s Lani Pallister securing victory in the women’s 400m freestyle at the Pan Pacific Championships have received a major boost after a disastrous heat swim from Summer McIntosh saw the world record holder miss the final.

In the biggest shock of the four-day meet in Irvine, two years out from the Los Angeles Olympics, the Canadian superstar could manage only the ninth-fastest time overall.

McIntosh finished third in her heat behind Pallister (4:05.22) in a time of 4:08.56, leaving her 0.2 seconds behind the eighth-fastest qualifier in China’s Fan Yaqi.

McIntosh was trying to conserve energy for Friday night’s final (midday Saturday AEST) but appeared shocked at missing the final of an event where she won a silver medal behind Ariarne Titmus at the 2024 Olympics. McIntosh’s time was 14 seconds slower than her world record.

The 19-year-old did not stop to speak to media after her race but addressed her swim on Instagram.

“I take full responsibility for my misjudgment in this morning’s heats,” McIntosh wrote.

She will race in the ‘B’ final but cannot win a medal.

Pallister, who has a personal best of 3:58.87 and won gold in the event at the recent Commonwealth Games, will square off against US great Katie Ledecky, who was the fastest qualifier in 4:03.48.

Ledecky and Pallister have posted similar times this year, with both breaking the four-minute barrier, but the American will probably start as a slight favourite.

Pallister produced a shock victory over McIntosh in the women’s 200m freestyle on night one, prompting questions about the Canadian’s form after illness forced her to withdraw from races at her trials.

McIntosh bounced back to win the 400m individual medley on day two – another event in which she holds the world record – ahead of Australia’s Jenna Forrester, but said afterwards she was unhappy with her performance.

Pallister is more of an 800m and 1500m specialist but said she was eager to test herself in the 400m.

“I had a pretty cruisy last 300 metres,” Pallister said after her heat. “My 400 [freestyle] is just sitting in this weird little space at the moment. I want so much more for that event.”

Meanwhile, Australian Sam Short is a big gold medal chance in the men’s 400m freestyle after qualifying fastest for the final in a time of 3:44.34.

“It’s going to be a hot race and way quicker than this morning,” Short said. “This will be a harder win than my 800. I have been flying in the 400 but [China’s] Zhang Zhanshuo is a better competitor than Bobby Finke at the moment.”

Tom Decent is the chief sports writer for The Sydney Morning Herald.Connect via X or email.