Sweden's Sarah Sjostrom heading for qualification in the women's 100m freestyle

Budapest (AFP) - Swedish great Sarah Sjostrom, who is seeking a first World Championships gold in the 100m freestyle, advanced from a depleted talent pool in the heats in Budapest on Wednesday.

While the 28-year-old Swede is trying to turn back the clock, the day could be dominated by a pair of youngsters, David Popovici and Leon Marchand, who are threatening world records in the evening finals.

Sjostrom has 17 World Championship medals. She has four in the 100m free, but none are gold. She qualified fourth fastest in the heats.

Australian teenager Mollie O’Callaghan set the best time.

Another Australian, the number two seed Shayna Jack, who had already won two relay medals as she returned to major competition in Budapest after a drug ban kept her out of the last worlds and Olympics, was a late scratch after an accident.

“Due to an unfortunate incident in this morning’s training session. I have broken my hand. I am broken hearted to announce that I have to withdraw from the rest of the competition,” Jack posted on social media.

She said she would focus on the Commonwealth Games in Birmingham later this year.

The field had already been winnowed with the top three in last year’s Olympics all out.

Champion Emma McKeon is also focusing on the Commonwealth Games, silver medallist Siobhan Haughey of Hong Kong has been knocked out of the championships by an ankle injury and Australian Cate Campbell is taking a year off.

Canadian Kelsey Wog was fastest in women’s 200m breaststroke qualifying

American Lilly King, the silver medallist in Tokyo, was second.

After King missed a medal in the 100m breast on Tuesday, her college coach, Ray Looze, told American media that she was racing at “80 percent of what her capability is.”

Olympic champion Tatjana Schoenmaker of South Africa is skipping these championships.

Another Olympic campion, Australian Zac Stubblety-Cook was narrowly quickest in the men’s 200m breaststroke heats, edging Dutchman Caspar Corbeau by 0.06sec.

American Shaine Casas topped qualifying in the men’s 200m backstroke ahead of 19-year-old Australian Joshua Edwards-Smith.

- Third world record -

Wednesday’s finals offer another sighting of three of the teenage breakout stars of the week and the tantalising possibility of a third world record in the championships.

Popovici, the 17-year-old Romanian who broke another world junior record in 100m freestyle qualifying. His big-name rival Caeleb Dressel withdrew after winning his heat for unspecified health reasons.

That leaves Popovici, who swam 47.13sec on Tuesday, chasing the world record of 46.91, set by Brazil’s Cesar Cielo in 2009, just before high-tech streamlined suits were banned.

There is a slim chance that Marchand could challenge Ryan Lochte’s 2011 record in the 200-medley final. The 20-year-old Frenchman swam the second fastest ever 400m medley when he won gold in that event on Saturday.

In the women’s 200m butterfly, the fastest qualifier, 15-year-old Canadian Summer McIntosh, is simply after her first gold to follow her silver in the 400m freestyle.