McIntosh in cruise control as Tatjana Smith eyes Olympic golden double
Already the 400m medley champion and 400m freestyle runner-up, the 17-year-old came home sixth fastest in 2mins 07.70secs at La Defense Arena behind Chinese pacesetter and defending champion Zhang Yufei (2:06.55).
A back-to-back world champion in 2022-23, McIntosh has been getting progressively faster and is now tied for the fifth best time ever.
But while in electric form, victory is by no means guaranteed in a bumper field spearheaded by veteran Zhang, who clocked the third fastest 200 fly in history to win Tokyo gold.
American Regan Smith took silver in Japan behind Zhang and remains a serious threat, posting the second best heat time.
"I was just trying to make semis and conserve as much energy as possible heading into tomorrow's final," said McIntosh, who had plenty left in the tank.
"For me really in race planning for 200 fly, I'm always really just trying to focus on myself and know that I can put down a good last 15m."
South Africa's Tatjana Smith is also gunning for more glory as she bids to become the first woman to win the breaststroke double since compatriot Penny Heyns at Atlanta in 1996.
Smith won Tokyo 200m gold in a world record 2:18.95 and is in red-hot form after securing the 100m title on Monday.
While her record was broken in 2022 by Evgeniia Chikunova, the Russian is not in Paris, leaving Smith top seed.
She touched in 2:21.57, 1.5 seconds clear of second-placed Dutchwoman Tes Schouten, the current 200m breaststroke world champion.
Kate Douglass, who dipped below 2:19 at the US trials, was third fastest with fellow American Lilly King, who took silver in Tokyo, 11th.
"I think the 100 really took off a lot of pressure in terms of a lot of expectations so now this time I can really just have fun with my swimming," said Smith, who indicated she could retire after Paris.
"We'll see, I'll tell you after the semis. Every race now I'm just enjoying and having fun."
Great shape
With Russian defending champion Evgeny Rylov another not at the Games, the men's 200m backstroke is wide open.
Switzerland's Roman Mityukov led the way into the semi-finals in 1:56.62, followed by Germany's Lukas Maertens, the 400m freestyle champion.
Tokyo silver medallist Ryan Murphy, Hungary's Hubert Kos and Spanish world champion Hugo Gonzalez also progressed.
So did 100m backstroke winner Thomas Ceccon of Italy, but the man who came second in that race, China's Xu Jiayu, was a no-show with his lane left empty.
"I'm not that confident (for 200), but after the 100, you know, I'm in great shape. I'm feeling good in the water," said Ceccon.
Britain's Tokyo bronze medallist Luke Greenbank won his heat but was disqualified.
The heat action comes ahead of a jam-packed finals session later where French hero Leon Marchand is bidding to win two more golds to go with his 400m medley title.
He will suit up in both the 200m butterfly and 200m breaststroke finals.
American great Katie Ledecky is a red-hot favourite to defend her 1,500m freestyle crown.
She has not only set the last six world records, but owns the fastest 19 times ever swum and is more than 18 seconds faster than her nearest competitor.
Should Ledecky prevail, it will be her eighth Olympic gold, and 12th medal overall.
The men's and women's 100m freestyle titles will also be decided with Australia's Mollie O'Callaghan and Romania's David Popovici aiming to do the double after winning the 200m finals.