The Canadian took her gold medal tally to three at the world championships in Singapore on Thursday, but it was clear from her reaction that her target had been Liu Zige's record of 2:01.81, a mark set in 2009 during the "supersuit" era.
McIntosh powered home 0.18 seconds behind Liu's mark in 2:01.99. A personal best (PB), a championship record -- but not good enough for the 18-year-old.
"Going into tonight, my coach and I, our big goal was to break that world record. It's what I've been training for," McIntosh said when asked about her reaction.
"To see that I missed it by that little, and I know that I messed up the last 15 metres of my race... Overall, happy with the time and a PB, but I didn't reach my goal tonight.
"It was a night in which we were aiming for the world record, which often I don't really focus on, but to see how close I was to breaking it and not getting it, I mean, I'm a little bit frustrated, but I can't be too hard on myself."
McIntosh came home three seconds ahead of American Regan Smith, while the bronze medal went to Elizabeth Dekkers, who was a last-minute addition to Australia's team.
"I really had no expectations and that was, I think, the happiest I've been walking out onto the pool deck," Dekkers, a silver medallist in the event in 2023, told Australian broadcaster Nine Network.
"That race hurt. Definitely not the best I've ever put together, but it was really fun and I had a great time."
McIntosh is aiming to match Michael Phelps's record of five individual gold medals at a single world championships. She still has the 800 freestyle and 400 individual medley to come.