It's taken less than a day for a new rule introduced in the Paris Olympics track events to be used cannily by an American athlete.

Freddie Crittenden's 12.93 seconds at the national trials just over a month ago is the fastest 110m hurdles time of 2024 and the 13th-fastest of all time.

He is one of Team USA's biggest medal contenders on the track, but when he came out of the blocks in his heat, the 30-year-old looked like he was running in treacle.

Early concerns of an injury or just missing the start were allayed as he trotted down the track and cleared every obstacle with perfect form, coming home in last place in a time of 18.27.

While that might have earned him bronze at the first modern Olympics in 1896, it was the slowest time in the heats by almost five seconds in the 2024 heats.

But Crittenden didn't look worried in the slightest after the race, because he knew he would get another shot with more chance to rest an injury.

"I didn't run hard because I had some aggravation yesterday in my adductor [muscle]. There's some activation that didn't work and that's caused pain and discomfort," he said.

"The plan was to use the repechage to get through the rounds, not get disqualified. Then I can run hard in the repechage round in two days, when hopefully the discomfort's gone.

What is a repechage?

Repechage, when loosely translated from French, means "second chance".

It's nothing new in track cycling, rowing, speed skating and a whole host of other events, but it is a new edition to the track and field events for Paris 2024.

At previous Olympics, the top three finishers in heats would progress automatically, with the remaining spots in the semifinals or final made up by the runners who finished fourth or lower with the best times.

But in July 2022, World Athletics announced a change at elite events, with all the non-automatic qualifiers (except for those who did not start, did not finish or were disqualified) going into repechage races to fill the remaining spots in those later races.

It is in place for the first time at an Olympic Games in Paris for the 200m through 1,500m races, plus the hurdles events.

As you'd expect, Crittenden has become a fan.

"It can be strategic. If I'd had to really go for it today to qualify I could easily have crashed out. I could have really hurt myself much worse. It would have been all or nothing," he said.

"The Olympics is the biggest event we have, the pinnacle. And for athletes to train really hard to get here and then have just one round to go for, it is really hard.

"This gives them another opportunity to represent their country and themselves, to show all the hard work they've done."

Why has athletics brought in repechage races?

According to World Athletics boss Sebastian Coe, it was to simplify things for athletes and build anticipation for fans.

"The repechage rounds will give more exposure to our sport during the peak Olympic period and will be carefully scheduled to ensure that every event on our Olympic programme retains its share of the spotlight," he said in 2022 when the change was announced.

We have already seen the first of the Olympic repechage races, in the women's 800m.

Australian Abbey Caldwell's season's best 1:58.49 was the sixth-fastest time across all six heats, but she was fifth in her race, which meant she had to go into a repechage race despite running faster than 18 of the 22 automatic qualifiers.

But she won her repechage by just 0.24 of a second to progress to the semifinals, which will be held on Monday at 4:35am AEST.

The men's 1,500m also went through the process on Sunday morning, but Australia's Stewart McSweyn, Oliver Hoare and Adam Spencer could not use it to their advantage the same way Caldwell did.

Torrie Lewis's second chance saloon

Australian sprint sensation Torrie Lewis will be hoping to do what Caldwell did in the women's 200m repechages.

Under the old system, 19-year-old Lewis would have been through to her first Olympic semifinal as the third-fastest non-automatic qualifier.

Instead, because she missed third by 0.1 of a second in her heat, she will run a repechage race, as will fellow Australian Mia Gross.

The winners of the four races plus the next two fastest will progress to the semifinals.

Torrie Lewis and Mia Gross are in the women's 200m repechages at 8:50pm on Monday. The men's 110m hurdles repechages are at 6:50pm on Tuesday.